Concrete is an erection material composed of cement, fine aggregates (sand) and coarse aggregates mixed with water. Portland cement is the mostly used cement for the production of concrete. It is the most popular artificial material. Probably It is used more than any other man-made product in the world.
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Its good to see a growing momentum in favour of reusing existing building structures and extending their lives, as the construction industry considers ways to reduce the amount of materials it consumes. Concrete lends itself well to this approach as can be seen by the number of buildings that have successfully been given a new lease of life. This years Pritzker Prize was won by Lacaton & Vassal partly for the transformation of three social housing buildings at Grand Parc in Bordeaux, where the concrete frames were upgraded and generous flexible spaces added to each unit.
The case study of 160 Old Streetalso shows how well an older concrete frame can be adapted to form the structure for a new building. In this case, 76% of the original structure was retained, reducing life-cycle emissions by 2,850 tonnes, while increasing the net lettable area of the building by 70%.
This kind of project is one approach to a circular economy, where the element that is repurposed is not individual beams or columns, but the entire frame. It is possible because concrete is a very durable material when used internally, designing for 50 years will give at least 100 years of useable life. Reuse is necessarily always a bespoke solution, and the decision in every case will depend on the unique circumstances of a specific building and the current requirements of the client and the market. But for structural engineers involved in potential reuse projects, there are several steps that will be key to a successful outcome.
When conducting an initial investigation into the potential for reuse, a first step is to look for record drawings. This will make a huge difference to the design of the modifications and will act as a useful reminder that the drawings and information we produce for new buildings or extensions today should be kept safe for future engineers. With a copy of the drawings, the checks required to analyse the frame for the new use and loadings becomes much easier.If the old drawings no longer exist, it will be necessarily to conduct investigations to check what is there. In particular, the following should be analysed:
Concrete continues to increase in strength as it ages, so even with the drawings to hand it is worth checking the concrete strengths. Another resource for checking existing concrete frames might be archive editions of Concrete Quarterly, which go back to 1947 and contain many detailed case studies. The full archive is available in PDF form here.
The concrete frame can then be backanalysed to check its capacity and to assess whether this will be sufficient for the new use. The codes of practice that were in use when the frame was built are very helpful in this respect (see table 1), but it is possible to use modern methods of analysis on an old frame. Strut-and-tie modelling is particularly helpful in this regard as it can show many possible load paths within the concrete (for more information, refer to Strut-and-tie Models, The Concrete Centre, 2015).
Broadly speaking, design concrete strengths have increased over theyears. In 1934, the ordinary grade concretes had strengths of 1620MPa. By 1985, BS 8110 assumed minimum strengths of 20MPa for reinforced concrete, 25MPa for precast concrete and 30MPa for prestressed concrete. Concretes in the 1980s were typically a cube strength of 30MPa for normal reinforced concrete frames.
Reinforcement grades and types have also changed with time. It is advisable to test reinforcement in buildings dating from before 1960, as it tended to be quite variable. Generally, plain round mild steel bars had a yield strength of 250MPa, with high yield deformed bars 415485MPa depending on the age and diameter. The Concrete Societys 2020 publication TR70 Historical approaches to the design of concrete buildings and structures is a very useful guide for the designer.
If a concrete structure does need to be strengthened, various methods can be adopted, from replacement of the over-stressed element to strengthening with additional reinforcement or carbon fibre. The 2012 Concrete Society publication TR55 Design guidance for strengthening concrete structures using fibre composite materials gives guidance on using fibre composites to strengthen both bending elements and columns. The confinement provided by wrapping the column with carbon fibre increases the capacity of the concrete significantly.
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Cement, in general, adhesive substances of all kinds, but, in a narrower sense, the binding materials used in building and civil engineering construction. Cements of this kind are finely ground powders that, when mixed with water, set to a hard mass. Setting and hardening result from hydration, which is a chemical combination of the cement compounds with water that yields submicroscopic crystals or a gel-like material with a high surface area. Because of their hydrating properties, constructional cements, which will even set and harden under water, are often called hydraulic cements. The most important of these is portland cement.
This article surveys the historical development of cement, its manufacture from raw materials, its composition and properties, and the testing of those properties. The focus is on portland cement, but attention also is given to other types, such as slag-containing cement and high-alumina cement. Construction cements share certain chemical constituents and processing techniques with ceramic products such as brick and tile, abrasives, and refractories. For detailed description of one of the principal applications of cement, see the article building construction.
Cements may be used alone (i.e., neat, as grouting materials), but the normal use is in mortar and concrete in which the cement is mixed with inert material known as aggregate. Mortar is cement mixed with sand or crushed stone that must be less than approximately 5 mm (0.2 inch) in size. Concrete is a mixture of cement, sand or other fine aggregate, and a coarse aggregate that for most purposes is up to 19 to 25 mm (0.75 to 1 inch) in size, but the coarse aggregate may also be as large as 150 mm (6 inches) when concrete is placed in large masses such as dams. Mortars are used for binding bricks, blocks, and stone in walls or as surface renderings. Concrete is used for a large variety of constructional purposes. Mixtures of soil and portland cement are used as a base for roads. Portland cement also is used in the manufacture of bricks, tiles, shingles, pipes, beams, railroad ties, and various extruded products. The products are prefabricated in factories and supplied ready for installation.
Cement is a binder of the construction materials, due to the adhesion and cohesion properties, it provides excellent bond strength to the concrete. Cement is mixed with filler materials like sand, aggregates that provide sufficient rigidity to the structure. When cement, fine aggregates, and coarse aggregates are mixed with sufficient water, concrete is formed. Various types of cement such as Ordinary portland cement(OPC), portland pozzolana cement(PPC), Rapid hardening cement, etc are available in the market.
Hydraulic cement is a type of cement that not only harden on reacting with water but also form water-resisting products. Cement on reacting with water commences the hydration reaction. Hydration reaction is the process by which the cement mixture gains its strength by forming various compounds with the evolution of heat.
Hydraulic cement can successfully be used inside the water for marine structures, water retaining structures, etc., There are 16 types of hydraulic cement that have been discussed in this article below.
1. Ordinary Portland cement(OPC),2. Portland Pozzolana cement(PPC),3. Rapid hardening cement,4. Extra Rapid hardening cement,5. Quick setting cement,6. Sulphate resisting cement,7. Low heat cement,8. Oil well cement,9. Blast furnace slag cement,10. Expansive cement,11. Hydrophobic cement,12. Masonry cement,13. Air entraining cement,14. High alumina cement,15. White cement,16. Coloured cement,
Non-Hydraulic cement is derived from the calcination of gypsum and calcium carbonates. Slaked lime is an example of non-hydraulic cement. These cement dont harden on reacting with water but by coming in contact with carbon dioxide. Carbon dioxide commences the carbonation reaction which sets the cement.
Ordinary Portland cement(OPC) is made by pulverising calcium silicate clinkers, calcium sulphates, and limestones at high temperatures. OPC consists of key elements called the Bogues compounds which are responsible for the strength gain and hardening of the cement. The names of the Bogues compounds and their composition in the ordinary Portland cement are as follows:
It is responsible for the rapid setting action of the cement It evolves moderate heat due to hydration reaction.OPC is a basic type of cement consisting of the Bogues components in the above proportions to gain the desired strength in 28 days. The different grades of Ordinary Portland cement are 33 grade, 43 grade, and 53 grade. The OPC 33 grade of cement will gain 33 MPa in 28 days and so on. The OPC can be stored for 3 months in a cool and dry place.
This type of cement is made of the Ordinary Portland Cement clinkers, gypsum and fly ash. Fly ash is a waste product from the thermal power plants. The advantages of using fly ash in the cement not only reduce air pollution but also increases the strength of the cement.
Flyash decreases the rate of strength gain in the early days. But the strength of the cement increases in the later stages. The fly ash reacts with the Calcium Hydroxide in the hydration products to form Calcium Silicate Gel (CSH gel) which is responsible for the strength of the cement. The PPC cement can be stored for 3 months in a cool and dry place.
Rapid hardening cement (RHC) also called High early strength portland cement. concrete has high percentages of Tricalcium Silicate (C3S) and low percentages of Di Calcium Silicate(C2S). This composition accelerates the hydration reaction leading to the rapid strength gain of the cement. Due to the increased lime content, 70% of the stipulated strength (7 days strength of OPC) can be gained in three days.
The strength attained by rapid hardening cement in 7 days is almost same as 28 days strength of opc. Due to the accelerated hydration reaction, the evolution of heat is high. Necessary actions must be taken to reduce the shrinkage cracks that may occur due to the high heat of hydration evolved.
Extra Rapid hardening cement is an enhanced version of the Rapid hardening cement. In addition to the composition of RHC, calcium chloride of weight not less than 2% is added to the cement. This accelerates the hydration process.
Some Extra Rapid hardening cement can gain as much as 15 Mpa and 25 MPa in 8 hours and 24 hours respectively. The concreting should be done within 20 minutes of mixing with water to prevent setting. This types of cement can be stored for a period of 1 month only after which it may lose its properties and become unusable.
Quick setting cement as the name suggests will have a quicker setting action. The setting action of this cement starts within 5 minutes as it becomes stone-hard in less than an hour. The natural retarder that slows the setting process in the cement is the gypsum.
The quantity of gypsum present in the cement is restricted to not more than 3% and accelerators like aluminium sulphate are added to speed up the setting action. Due to the increased sulphate content, the risk of sulphate attack is elevated. It is also very expensive and demands great care in placing the concrete.
The aluminates present in Bogues compounds react with the sulphates in the soil or water to form high volume products like calcium sulphate and Calcium Sulpho Aluminate. Due to the amplified volume, the internal pressure increases and as a result cracks are formed. This is called Sulphate attack.
Low heat cement produces low heat of hydration during the strengthening process. Excess heat of hydration may trigger pre-mature shrinkage cracks. The heat evolution can be controlled by reducing the heat producing Bogues compounds.
The tricalcium silicate (C3S) and tricalcium Aluminate (C3A) are reduced and Dicalcium Silicate (C2S) is increased to achieve sufficient strength with low heat evolution. Due to the retarded hydration process, the early strength gain is less but the required strength is gained at the later stages.
Oil well cement is used in the process of oil well drilling. During the drilling process, steel casings are inserted inside the holes. The surrounding earth around the steel casings may not be continuous and stiff. Any discrepancies in the surrounding soil will increase the risk of escaping of the invaluable gases or oil.
In order to prevent it, the oil well cement is used to reinforce the earth surrounding the drill hole. This cement should be able to flow to greater depths and withstand a temperature of minimum 175 degree centigrade and a pressure of at least 3000 kg/cm3. This can be achieved by adding retarders like starch and cellulose to the cement.
Blast Furnace slag cement is made up of the Ordinary Portland Cement clinkers, gypsum and Ground Granulated Blast Furnace Slag (GGBS) added in certain proportions. The GGBS is a waste product from the steel manufacturing industry. Using the Ground Granulated Blast Furnace Slag will not only reduce the pollution levels but also has the following
Expansive cement is made up of Ordinary Portland Cement clinkers, expanding agents, and stabilising agents. Cement, contracts on hardening which may cause non-structural cracks in the structure. This contraction can be avoided by using expanding agents like sulpho aluminate clinkers. Expanding agents must always be accompanied by stabilising agents like calcium chloride or pozzolana to prevent over expansion.
Hydrophobic cement is made by grinding Ordinary Portland Cement clinkers, gypsum, and water-repelling substances like stearic acid and oleic acid in the manufacturing process itself. These repellents form a film around the materials of the concrete and produce a water-repelling mix.
For increased efficiency, vigorous mixing of the aggregate is recommended to break the film and initiate the hydration reaction. This cement can be stored for longer periods even in cold weather regions because of the water-repelling film around the cement particles.
Masonry cement is made up of Ordinary Portland Cement clinkers, gypsum, limestone and air-entraining agents. Based on the requirements, water-repellent additives may also be added to the cement. Masonry cements are used for preparing the mortar for building the masonry structures stone masonry or brick masonry. It is not widely used.
Air entraining cement is made up of Ordinary Portland Cement clinkers, gypsum, and air entraining agents. The need for air entraining agents is prominent in cold weather regions that are vulnerable to freeze thaw cycles.
The liquid water penetrating into the cement structure under freezing temperatures will turn into solid ice. The volume occupied by the solid ice is greater than that of the liquid water thus increasing the internal pressure.
As a result, cracks will be formed to release the pressure. This is called the freeze thaw cycle. This can be avoided by using air entraining agents like wood resins, hydrogen peroxide, aluminium powder, sulphonic acid, etc., These air entraining agents will form artificial air pockets inside the mix. Air entraining admixtures can also be added to ordinary cement to achieve the same results.
These air pockets can make up to the extra space needed by the formation of ice. This increases the durability of the structure but obviously the air pockets will reduce the strength of the concrete. Air bubbles should not be more than 3 to 4 % than the volume of the concrete.
High Alumina cement is obtained by adding alumina (at least 32% to 80%) to the Ordinary Portland Cement clinkers. This cement is also known as the calcium aluminate cement. This is made by pulverising calcium aluminate clinkers alone. Unlike other hydraulic cement, high alumina cement does not have Tricalcium Sulphate and Dicalcium sulphate as the base material.
The grey colour of the cement is caused by the presence of Iron oxide. By reducing the amount of Iron oxide in the cement to less than 1%, white cement can be obtained. White cement is made by using high purity limestone and china clay both of which are known to have low iron content. It is expensive than ordinary cement. The fineness of white cement is greater than that of normal cement.
Various colours can be imparted to the cement by adding mineral pigments. For example, adding cobalt induces blue colour, chromium gives green colour and various proportions of iron oxide give grey, brown and red colour.
OPC 33, 43 and 53 grade, Portland pozzolana cement, Portland Slag Cement (PSC) Rapid Hardening Cement Sulphate Resisting Portland Cement (SRC) Low Heat Portland Cement Hydrophobic Portland Cement, White Cement and coloured cement.
Concrete is the most common used man-made material on earth. The uses of concrete range from structural applications to piping, drains, and pavers. Buildings, bridges, roads, and more could not be constructed without this important material.
Concrete mixing plants must perform regular maintenance on mixers to ensure proper working conditions and efficiencies. Maintenance can involve accessing the mixers entry points for cleaning and servicing of paddles or blades. To ensure work safety, power must be isolated prior to entry of the mixer and at no time during maintenance can power be inadvertently re-energized.
Trapped key interlock safety solutions ensure a pre-determined sequence of operations each & every time. While LOTO provides a visual warning and identifies hazards, a TKI solution physically prevents a specific set of actions from being performed until previous action(s) have been fully completed!
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Hydraulic Cement is a product used to stop water and leaks in concrete and masonry structures. It is a type of cement, similar to mortar, that sets extremely fast and hardens after it has been mixed with water. Hydraulic cement is used widely in the construction industry sealing structures below grade and in situations where structures can be affected or submerged in water.
Hydraulic cement should be applied to surfaces that have been cleaned, free of oil, dirt, grease or any other contaminant that will affect the bonding with the permanent structure. These are the steps for a successful application:
The words cement and concrete are often used interchangeably. However, cement is actually an ingredient of concrete, not the final product. Cement is important becasue it binds, or holds, the concrete mix together, giving it strength.
Portland Cement is a type of cement, not a brand name. Many cement manufacturers make Portland Cement. It is a basic ingredient of concrete, made using a closely controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other ingredients to which gypsum is added in the final grinding process to regulate the setting time of the concrete. The Portland Cement Association's How cement is made provides detailed information of the process. To find out more about what concrete is made of, concrete mix designs, admixtures, and water to cement ratios, read our section "What Is Concrete?" Portland Cement Association Type 1 - Normal portland cement. Type 1 is a general use cement. Type 2 - Is used for structures in water or soil containing moderate amounts of sulfate, or when heat build-up is a concern. Type 3 - High early strength. Used when high strength are desired at very early periods. Type 4 - Low heat portland cement. Used where the amount and rate of heat generation must be kept to a minimum. Type 5 - Sulfate resistant portland cement. Used where the water or soil is high in alkali. Types IA, IIA and IIIA are cements used to make air-entrained concrete. They have the same properties as types I, II, and III, except that they have small quantities of air-entrained materials combined with them. Types IL, IS, IP and It are blended hydraulic cements that offer a variety of special performance properties. A cement factory (Juan Enrique del Barrio / Shutterstock). These are very short descriptions of the basic types of cement. There are other types for various purposes such as architectural concrete and masonry cements, just to name two examples. Your ready mix company will know what the requirements are for your area and for your particular use. Simply ask them what their standard type of cement is and if that will work fine for your conditions. WATER TO CEMENT RATIO: THE #1 ISSUE AFFECTING CONCRETE QUALITY A low water to cement ratio is the number one issue effecting concrete quality. The ratio is calculated by dividing the water in one cubic yard of the mix ( in pounds) by the cement in the in the mix (in pounds). So if one cubic yard of the mix has 235 pounds of water and 470 pounds of cement- the mix is a .50 water to cement ratio. If the mix lists the water in gallons, multiply the gallons by 8.33 to find how many pounds there are in the mix. Low water cement ratio impacts all the desired properties of hardened concrete listed in desired properties of concrete. Use a maximum .50 water to cement ratio when concrete is exposed to freezing and thawing in a moist condition or to deicing chemicals per the 1997 Uniform Building Code. (Table 19-A-2) Use a maximum .45 water to cement ratio for concrete with severe or very severe sulfate conditions per the 1997 Uniform Building Code (Table 19-A-4) Water permeability increases exponentially when concrete has a water cement ratio greater than .50. Durability increases the less permeable the concrete mix is. Strength improves with lower water cement ratios. A .45 water cement ratio most likely will hit 4500 psi (pounds per square inch) or greater. A .50 water cement ratio will likely reach 4000 psi or greater. For complete Uniform Building Code information regarding concrete construction, review with your architect, your ready mix supplier, or at your local library.
Types IA, IIA and IIIA are cements used to make air-entrained concrete. They have the same properties as types I, II, and III, except that they have small quantities of air-entrained materials combined with them. Types IL, IS, IP and It are blended hydraulic cements that offer a variety of special performance properties.
Your ready mix company will know what the requirements are for your area and for your particular use. Simply ask them what their standard type of cement is and if that will work fine for your conditions.
The ratio is calculated by dividing the water in one cubic yard of the mix ( in pounds) by the cement in the in the mix (in pounds). So if one cubic yard of the mix has 235 pounds of water and 470 pounds of cement- the mix is a .50 water to cement ratio.
Strength improves with lower water cement ratios. A .45 water cement ratio most likely will hit 4500 psi (pounds per square inch) or greater. A .50 water cement ratio will likely reach 4000 psi or greater.
Ultra-High Performance Concrete (UHPC) is a new class of concrete that is exceptionally strong and durable. It is not only ideal for traditional applications of regular concrete, but it also allows for new applications of concrete in areas such as contemporary design that involve thinner components or complex shapes.
The Ultra-High Performance Concrete market size is expected to grow at a compound annual growth rate (CAGR) of 7% between 2017 and 2023, according to a report published by Market Research Future. This is not surprising given the many uses and benefits of UHPC and the encouragement of its use by the Federal and state governments for many infrastructure projects.
According to the Federal Highway Administration (FHWA), UHPC is defined as a cementitious composite material of an optimized gradation of granular constituents, a water-to-cementitious materials ratio less than 0.25, and a high percentage of discontinuous internal fiber reinforcement.
In UHPC, integrated fibers are added to the concrete mix. The fibers vary from polyester to fiberglass bars, basalt, steel, and stainless steel. Each of these integrated fibers create a progressively stronger end product, with steel and stainless steel delivering the greatest gains in strength.
UHPC became commercially available in the United States in 2000. It has already been used in many state infrastructure projects, and it is being considered for use in many future projects given its longevity and lower lifecycle cost. For a full list of UHPC bridges in the United States, consult this resource from FHWA.
The FHWA also advocates the use of UHPC through its Every Day Counts (EDC) program. EDC identifies and utilizes innovative technologies to reduce project timelines, increase safety, reduce traffic delays, and lessen the environmental impact of construction at the state and local levels.
Every two years, the FHWA works with state and local transportation departments, governments, and other vested parties to identify the latest innovations to support. The EDC-3 Innovations for 2015-2016 and the EDC-4 Innovations for 2017-2018 include the use of UHPC connections for prefabricated bridge elements and systems (PBES), making it a favored concrete technology for these applications.
Ultra-High Performance Concrete vastly widens the possibilities for applications of concrete. The combination of its strength, durability, flexibility, and resistance to damage from the elements makes UHPC clearly favorable to regular concrete. Projects last longer and require less upkeep and maintenance. Projects can also be completed faster with less interruption to local traffic patterns and environmental damage. The U.S. government clearly values UHPC and the many benefits it brings to infrastructure projects, making it an important concrete technology for builders and contractors to learn about and use.
Cor-Tuf UHPC, the exclusive licensed producer of Cor-Tuf Ultra High Performance Concrete (UHPC) in the United States and the world, is the ideal material to use in the Federal Governments proposed $2 trillion plan to rehabilitate and upgrade the American infrastructure. And, thanks to our latest innovationour UHPC mobile batch plantCor-Tuf UHPC can now be used anywhere and everywhere, without any special considerations or accommodations.
The Federal Government has been putting a lot of emphasis on its proposed U.S infrastructure plan. The plan calls for a $2 trillion investment to repair the countrys damaged infrastructure, combat climate change, and create jobs.
Cor-Tuf UHPC, the exclusive licensed producer of Cor-Tuf Ultra High Performance Concrete (UHPC) in the United States and the world is bringing Cor-Tuf UHPC into mainstream production with its groundbreaking UHPC mobile batch plant. Now Cor-Tuf UHPC can be used by contractors anywhere and everywhere, under any conditions.
Believe it or not, concrete overlays have been in use in the U.S. for more than a century, with the first use dating back to the early 1900s. Concrete overlays were first used to build new highways and roads in our country, but later on the focus changed to using overlays as a cost-effective way to extend the life of roads and bridges that were past their prime.
If youve ever wondered, What is the difference between concrete and cement? youre in luck. The terms concrete and cement are often used interchangeably. But the truth is, they are not the same. In fact, that cement truck many of us refer to on a job site is actually a misnomerit is really a concrete truck.
Green concrete is a revolutionary topic in concrete technology history. Green concrete was first developed in Denmark in the year 1998. Green concrete has nothing to do with color. Green concrete is the type of concrete that is much like traditional concrete but the production of such concrete needs a minimum amount of energy and causes the least harm to the environment. Green concrete is a concept of using eco-friendly materials in concrete hence, green concrete is also known as eco-friendly concrete or environmentally friendly concrete.
Green concrete is very inexpensive to produce because; it is made with the use of waste materials as one of its components. The size of the construction industry all over the world is growing at a faster rate. The huge construction growth boosts demand or requirements for construction materials.
Aggregates are the main constituent of concrete. Because of continuously mining the availability of aggregates has emerged problems in recent times. To overcome this problem, there is a need to find a replacement to some extent and the solution to these problems is Green Concrete.
Concrete which is made from concrete wastes as one of its components that are eco-friendly is called Green Concrete. Concrete that uses less energy in its production and produces less carbon dioxide (CO2) than conventional concrete is green concrete.
The goal of the center for Green Concrete is to commute the environmental impact of concrete. To enable this, new technology is developed. The technology considers all aspects of a concrete constructions life cycle, i.e. structural design, specification, manufacturing, and maintenance.
Open Access is an initiative that aims to make scientific research freely available to all. To date our community has made over 100 million downloads. Its based on principles of collaboration, unobstructed discovery, and, most importantly, scientific progression. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. How? By making research easy to access, and puts the academic needs of the researchers before the business interests of publishers.
We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the worlds most-cited researchers. Publishing on IntechOpen allows authors to earn citations and find new collaborators, meaning more people see your work not only from your own field of study, but from other related fields too.
Zeolites have been widely used in various industries, leading to a high commercial value; this is mainly due to the wide diversity of naturally occurring species and the ability to synthesize new types. In the cement and concrete industry, natural zeolite is a popular natural pozzolanic material in some regions of the world owing to their economic, environmental, and technical advantages, among others, used pozzolanic materials. Many works have reported the use of natural zeolite as substituent material for cement in mortar and concrete. Generally, the use of natural zeolite can overcome environmental and economic problems associated with the use of high quantity of cement; furthermore, it is shown a strength enhancement and durability improvement properties of cement and concrete composites. In this context, this chapter strives to review the application of natural zeolite as pozzolan in cement and concrete composites, its characteristic, its proper incorporation, and each of the influencing parameters. In addition, the elaboration methods, textural and mechanical characterization, and applications of these composites will be treated.
The number of zeolites is constantly increasing; currently, the commission of structures of the International Zeolite Association (IZA) recognizes 232 unique structures that have been approved and have been assigned three letters of code . The chemistry of zeolite has been a subject of significant interest due to the ion exchange properties of zeolite, crystallinity, thermal stability, and well-defined molecular size closed structures . The code ASTM-618 (American Society for Testing Materials) defines pozzolans as siliceous or aluminum-siliceous materials, which by themselves have little to no cementing value, but when they are finely divided and in the presence of water and calcium hydroxide (Cal), they react chemically at room temperature to form cementitious agents .
Concrete made from Portland cement is the most widely used construction material today, mainly due to its cost-benefit ratio, in terms of compressive strength. Its manufacture involves the release of approximately 900kg of carbon dioxide per 1000kg of produced cements. Likewise, this amount of cement demands the use of 1693kg of water and 4798MJ in energy resources . This is the importance of reducing the environmental impact that the manufacture of the same produces. The use of mineral additions in the production of concrete is a technologically possible alternative. However, its use requires high standards of assurance and quality assurance, similar to those of cement .
The extent of the benefits provided by the use of blended cements increases with increasing content of additives in blended Portland cements. However, the content of additives in blended Portland cements, especially for natural pozzolans, is limited by some factors, such as an increase in water requirement and a decrease in the rate of strength development of the cementitious systems. It has been found that the blended cements containing high volume (55% by weight) of natural pozzolans (volcanic tuff) possess lower 28-day compressive strength when compared to the reference Portland cement, although they show similar strength values at 91days of age [6, 7]. Therefore, the production of high-volume natural pozzolan blended cements, which are able to compete against ordinary Portland cement, requires natural pozzolans exhibiting significantly high-strength activity.
In this chapter, we intend to review the literature available on these topics, addressing structural, mineralogical, and morphological properties, in the case of zeolites, and manufacturing processes, characterization, evaluation, and application, in the case of cement. As well each of the parameters influences the formation of cementing pastes, such as hydration, porosity, transport properties, durability, and carbonation, among others.
Pozzolans are materials with an amorphous and aluminous siliceous or siliceous content, which react with calcium hydroxide in the presence of water to form cementitious hydration products . Among the most common natural pozzolanic materials, such as fly ash and silica fume, is zeolite, which is used in some regions of the world, due to its lower cost and accessibility [9, 10]. Zeolites generally show pozzolanic activity due to their structural characteristics, and their use as additions in cements provides additional technical advantages to construction materials .
The pozzolanic properties of natural zeolites are determined by their high sorption ability, ion exchange potential, and specific structure. Their action involves various steps, including cation exchange; dissolution and/or breakdown of the zeolitic structure; possible formation of transient gel phases; and precipitation of hydrated calcium silicates and aluminates .
There are different methods of work for the evaluation of pozzolanic activity. In general, these methods are classified as indirect or direct, depending on the parameter to be studied . Direct methods monitor the presence of Ca(OH)2 and its subsequent reduction in abundance over time, as the pozzolanic reaction proceeds, using analytical methods such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), or assessment chemistry.
The Frattini test is a commonly used direct method involving chemical titration to determine the concentrations of Ca2+ and OH dissolved in a solution containing Portland cement andthe test pozzolan. This method has been used to measure the pozzolanic activity of metakaolin , catalytic cracking residues , fly ash , and zeolites .
The saturated lime method is a simplified version of the Frattini test, in which pozzolan is mixed with a saturated solution of lime (slaked lime, Ca(OH)2) instead of Portland cement and water. The amount of lime set by the pozzolan is determined by measuring the residual dissolved calcium .
Indirect test methods measure a physical property of a test sample, which indicates the degree of pozzolanic activity. This may involve the measurement of properties such as compressive strength, electrical conductivity, or heat evolution by conduction calorimetry. The results of an indirect pozzolanic activity test are often corroborated by direct tests to confirm that pozzolanic reactions are occurring [19, 20, 21, 22].
Zeolites naturally occur from volcanic origin and belong to the family of hydrated aluminosilicates. Their microporous structures can accommodate a wide variety of cations, which compensate the negative charge created by the substitution of Si by Al. Therefore, natural zeolites appear as cation exchangers in many applications, thanks to this property. Some of the main applications of zeolites in this area include the selective treatment of wastewater, extraction of ammonia, odor control, extraction of heavy metals from nuclear, mining and industrial wastes, soil conditioning for agricultural use, and even as an additive for animal feedstock .
Among all identified zeolites, clinoptilolite is the most abundant natural zeolite. In the structure of the zeolite, there are three relatively independent components: the aluminosilicate system, the interchangeable cations, and the zeolitic water. The simplified empirical formula of zeolites is:
where xcan vary from 0 to 0.5 and Mn+ represents Alkali and alkaline earth metals. The structure of aluminosilicates is the most conserved and stable component and defines the type of structure water molecules that can be presented in voids of large cavities and joined between ion systems and ions interchangeable through aqueous bridges. Water can also serve as a bridge between interchangeable cations.
The channels of the natural zeolites are predominantly occupied by Na+, K+, Ca2+, and H2O, as well as traces of Mg2+, Ti4+, Pd2+, K+, and Ba2+. Among them, Na+, K+, Ca2+, and Mg2+ can be exchanged with NH4+ions. The type and density of interchangeable cations influence the stability of the cavities and the thermal behavior of a zeolite [24, 25, 26, 27].
Concrete is more durable against elevated temperature and fire effects than many other construction materials. Although ordinary concrete is considered to have a satisfactory fire resistance, it can lose 4060% of its original strength upon exposure to 500C . Bilim  reported mortars containing zeolite show generally better performance to high temperatures about 900C.
Negative thermal expansion (NTE) is an unusual phenomenon in which materials shrink in volume when heated (or expand when cooled). It has only been observed in a small number of solids, including some metallic oxides, cyanide metal, polymers, and zeolites . It is important to understand how zeolites behave as a function of temperature. In recent years, research has been carried out on NTE in purely siliceous zeolitic structures [31, 32] and with a little less attention [31, 33] to aluminum-containing zeolites, in which it is known that structures and properties are particularly sensitive to extra-structural charge balancing cations and host molecules in the pores.
Water is an important guest molecule in the pore system of natural and synthetic zeolites. Adsorbent and catalytic properties of zeolites are also strongly affected by their water content. Cations seek the most energy-stable positions, and these positions play an important role in the catalytic activity.
This subject was investigated by Ili and Wettstein , who examined three distinct temperature ranges for volumetric thermal expansion. Associates with the dehydration of coordinated water molecules and with transverse vibrations of bridging oxygen atoms result in the reduction in the bonding angle.
As already mentioned, zeolite is a porous solid with a large capacity to house water molecules and can be used as a pozzolanic aggregate. The efficiency of porous aggregates as an internal curing agent in concrete depends on its water absorption and desorption characteristics. The desorption behavior of zeolite and other porous aggregates depends on the structure of their pores and mainly on the porosity size distribution. In general, a thick pore structure will lead to better desorption behavior [35, 36, 37].
Ghourchian etal.  were conducted a study of the performance of the porous aggregates and concluded that the water desorption of the zeolites is closely related to their microstructure. For a proper desorption, a thick-pored structure is needed with a high proportion of well-interconnected pores. While, in the case of zeolites, despite having a high-water adsorption capacity, they have a fine pore structure, which leads to retaining the water absorbed.
Zeolites are selective adsorbents for the removal of carbon dioxide, water vapor, and other impurities from the mixtures. The impurities adversely affect the capacity of the adsorbents used for the separation or purification. Water is a strongly adsorbed component in zeolite .
Due to the nature of the cation exchange, natural zeolites show a high performance in the adsorption of cations in aqueous solution such as ammonium and heavy metals. However, zeolites show varied ion selectivity and competitive adsorption for multicomponent system . In addition, these materials are not good adsorbents for the adsorption of anionic and organic ions. Surface modification with cationic surfactant can change the surface charge of the natural zeolite, making them applicable for adsorption of anions and organics. Most zeolites when heated give off water continuously rather than in separate stages at certain temperatures. The dehydrated zeolite can then reabsorb the original amount of water when exposed to water vapor. Recent investigation has shown that some zeolites such as phillipsite and gismondite lose and gain water in a stepwise manner. All-silica zeolites are chemically and hydrothermally more stable than aluminum containing ones and are therefore preferred for membrane application, including for dehydration, even though these types of membranes are hydrophobic .
The adsorption characteristics of any zeolite depend on the detailed chemical/structural composition of the adsorbent. The Si/Al ratio, the type of cation, the number, and the location are particularly influential in the adsorption. These properties can be modified by various chemical treatments to improve the separation efficiency of the natural raw zeolite. Acid/base treatment and impregnation with surfactant by ion exchange are commonly used to change the hydrophilic/hydrophobic properties for the adsorption of various ions or organic .
In general, the higher the cement replacement by natural zeolite has the lower the compressive strength. However, the percentages of reduction in resistance generally decrease with increasing age in cement. This behavior may be related to the pozzolanic activity of the natural zeolite. In terms of compressive strength, it appears that natural zeolite performs better in mixed cement compounds with lower water-cementitious material (w/cm) ratio .
In term of compressive strength, it seems that natural zeolite performs better in blended cement composites with lower w/cm ratios. Ahmadi and Shekarchi  showed that the concretes containing natural zeolite with a w/cm ratio of 0.40 displayed higher compressive strength than the control mixture at the ages of 3, 7, 28, and 90days, whereas contrary results were obtained for the concretes with a w/cm ratio of 0.5in the present study. Markiv etal.  showed, recently, that the substitution of cement by zeolite resulted in some reduction in strength until 90days of hardening, but after 180days, compressive strength of concretes containing zeolite exceeds the strength of concrete without zeolite.
Uzal and Turanl  reported the similar compressive strength of mortar with 55% zeolite in the binder to that of 100% Portland cement mortar, but this could only be achieved using superplasticizers. Karakurt and Topu  found 30% replacement of Portland cement by zeolite in their blended cement mortars as optimum; the compressive strength was similar to the reference mortar. Valipour etal.  observed a fast decrease in the compressive strength of concrete with the increasing amount of zeolite (1030% of the mass of Portland cement) in the mix, even with an increasing superplasticizer dosage.
It is generally recognized that the addition of pozzolan reduces the calcium hydroxide content in cement paste and improves the permeability of concrete . The most important concerns in the design of durable concrete are the alkali-silica reaction (ASR) and sulfate attack.
ASR causes the premature deterioration in concrete. Alkali hydroxides present in the concrete pore solution react with amorphous or poorly crystalline silica phases in aggregates, forming a gel that imbibes water and expands . The expansive pressure generated by the hydrated alkali silicate has been widely believed to induce cracking and deterioration of concrete. However, this notion may not be necessarily correct. Concrete is a porous material, and the hydrated alkali silicate is rheologically a fluid material that can slowly diffuse into the pores and preexisting cracks to lose its expansive pressure. The diffused alkali silicate has been proposed to generate an expansive pressure by reacting with Ca2+ ions .
The transport properties of concrete with the addition of zeolite have been studied by Ahmadi and Shekarchi  and Najimi etal. , who found a significant reduction in the penetration of water and chlorides, in the concrete with natural zeolite. On the other hand, Valipour etal.  reported that water sorptivity and gas permeability increase with the increase of zeolite in the mixture. Similar results were obtained for the oxygen permeability of Ahmadi and Shekarchi  but only for the dose of zeolite greater than 10%.
The liquid water transport parameters increase with the increasing addition of zeolite in the mixed binder. This is due to the pore distribution, that is, the volume of capillary pores, which is the most important factor, in the capacity of a porous medium to transport water in liquid form. In studies conducted by Vejmelkov etal. , it was found that, for lower zeolitic contents, up to 20%, the values of water absorption coefficient and apparent moisture diffusivity were still acceptable. However, for high levels of cement replacement, the acceleration of water transport is so high that it could present a concrete durability risk.
Ahmadi etal.  reported that natural zeolitic addition in concrete results in better water absorption, water penetration, and electrical resistivity, and the ternary mixtures containing natural zeolite with silica fume or fly ash perform best in water permeability and chloride penetration tests.
The durability of a concrete is a determining feature for its use, and this is due to the different corrosive environments to which it is exposed, including marine construction or hydraulic engineering. One of the important factors of this characteristic of concrete is the type of cement. It has been shown that the use of pozzolanic additives for cements increases their resistance to corrosion, due to the high impermeability, the decrease in the content of Ca(OH)2, and the reduction in the presence of capillary pores in the matrix. In fact, it hinders the penetration of aggressive media . Concrete can be attacked by acids both internally and externally. The existence of different kinds of acid in the environment around the concrete causes a great reduction in the pH of the concrete, and the reaction between the acids and the hydrated and unhydrated cement finally leads to the deterioration of the concrete. The primary effect of any type of acid attack on concrete is the dissolution of the cement paste matrix .
Maolepszy and Grabowska  carried out a study dedicated to studying the sulfate resistance of a cementing paste with zeolitic addition. They confirmed the beneficial effect of the zeolitic additive for cement mortars because those containing zeolite did not show visible damage in the surface in an aggressive solution of sulfate, while in the mortar that did not possess it, I present surface microcracks pronounced. Exfoliation of corners and colors changes (yellow and gray incursions on the walls of the samples).
The contraction is a phenomenon in which the concrete reduces its volume with time. The internal and external drying of the concrete is the main factor that causes the contraction. Internal drying, also known as self-desiccation, is caused by the consumption of water in the hydrating cement paste and the resulting creation of interfacial menisci between the pore fluid and the vapor in progressively smaller pores . The creation of meniscus leads to the accumulation of capillary pressure that puts the solids under compression and causes a macroscopic contraction, called autogenous contraction [56, 57]. External drying takes place due to the evaporation of water from the surface of the concrete to the ambient air or due to the migration of water to adjacent members. The evaporation of moisture from the surface of the fresh concrete can cause cracking of the plastic shrinkage , and a greater moisture loss of the hardened concrete can cause shrinkage by drying .
Generally, the durability properties of concrete improved by partial replacement of cement with natural zeolite. However, the concrete that contains 15% of natural zeolite achieves a suitable drying shrinkage. The latter does not have a satisfactory performance in the acid environment .
The pores can have an effect on the properties of the material in different ways. The compressive strength is primarily related to the total porosity, the size of pores and their distribution, the size and form of the biggest pores, and the relation between the pores. Shrinking is the function of energy exchange on the surface of pore walls. Durability depends on freeze-thaw resistance and is controlled by the volume of air entrained in the pores and spaces between the pores .
Water absorption and freeze-thaw resistance of hardened cement paste depend on the size of pores and capillaries, their type and distribution, and the closing of the pores. Closed and small pores are not filled with water completely. Pores that are not filled up with water are called reserve pores. In freezing conditions, some water from fully filled pores may move to these reserve pores and thus create a space for ice expansion. The distance between filled and unfilled pores must be small, so that the freezing water would move from filled to unfilled pores .
Capillary pores in hardened cement paste are formed through the evaporation of excessive water used in producing the cement paste. Usually, the cement paste is made using more water, and it is necessary for chemical reactions that occur during the setting of concrete. According to A.K. Kallipi, capillary pores are open and easily fill with water. The destructive effect during freezing depends on the amount of water in hardened cement paste. Presumably, the bigger amount and size of the pores reduce the freeze-thaw resistance of concrete. Furthermore, it is important to mention that the concrete prepared with saturated and dry recycled aggregates exhibits poorer freeze-thaw resistance, whereas better results obtained from the concrete made with the semi-saturated aggregates .
When a cementitious paste begins to harden with an air cure, and after the first minute of hydration, it is subjected to the action of carbon dioxide ions CO32contained in the air, which reacts with Ca2+ions of the portlandite, ettringite, and the silica gel of calcium in the form of Ca-carbonates CaCO3. This carbonation of the hydrate products is provided in the following schemes :
The air-curing conditions normally increase carbonation and cause incomplete hydration, self-neutralization, and drying shrinkage. These effects are most probably caused by decreasing the capacity for retaining sufficient water during the hydration and pozzolanic reactions. The depth of the carbonate layer formed depends on the contact time with CO2and its concentration in the surrounding environment as well as the diffusion coefficient of the hardened cement paste [63, 64, 65]. As the air-curing conditions are more important for long-term reactions than for short-term ones, the C2S phase, which usually reacts after 21days, is the most readily affected cement phase. The volume changes, which accompany the carbonation processes, lead to the filling of empty pore volumes with Ca carbonates and densify the structure of the hardened cement paste. Groves etal. , the microstructure of hardened pastes of C3Sand a smoke mixture of C3S/silica by TEM, before and after partial carbonation in a pure CO2atmosphere, concluded that calcium carbonate forms mainly in the outer product regions such as microcrystalline vaterite or calcite, which leads to a substantial level of carbonation of pulp in a day with a little additional carbonation in the coming days. The depth of penetration of CaCO3in the cement matrix depends on the time of contact of carbon dioxide and its concentration in the medium and on the coefficient of diffusion .
Lilkov etal.  have studied the early hydration of the cement, mixed with additives of natural zeolite (clinoptilolite), and they concluded that the process of carbonation on the surface of the cement paste takes place directly between the calcium ions of the solution and the carbon dioxide of the air without the formation of portlandite and ettringite. The depth of the carbonate layer formed depends on the contact time with the CO2and the rate of diffusion through the formed layer, where the crystallite size of the calcite is reduced overtime days.
The main causes of reinforcing steel corrosion are reacted with various aggressive agents, such as atmospheric carbon dioxide and chloride ions, and chemical attack throughout the service life of the concrete . In ordinary Portland cement, these harmful effects can be reduced by substitute pozzolans . Under a corrosive environment, concrete properties can be improved by using pozzolans such as zeolite and diatomite .
Steel rebars are protected against corrosion by both chemical and physical mechanisms. The chemical protection is provided by the concrete high pH (1213), which promotes the formation of a passive film on the steel surface. On the other hand, concrete acts as a physical barrier, hindering the access of aggressive agents. However, oxygen, water, chlorides, and/or carbon dioxide can be transported through concrete, reaching the rebars and inducing the corrosion attack. The chloride ions, when above a threshold value, provoke a local breakdown of the passive film and pitting corrosion. Carbon dioxide and its hydrolysis products react with the alkaline species present in concrete, leading to pH values as low as 9 .
Ahmadi and Shekarchi  found a positive effect of zeolite in cement mortar on the resistance to alkali-silica reaction. Janotka and Kraji  reported an improvement of sulfate corrosion resistance of zeolite-containing concrete. Similar effects of zeolite on alkali-silica reaction and sulfate resistance were observed by Karakurt and Topu . On the other hand, Najimi etal.  reported a significant strength reduction of zeolitic concrete after exposure to sulfuric-acid environment, that is, ~20% after 356days when compared with ~5% for reference Portland-cement concrete.
Besides eco-friendly, concrete should be sustainable and durable due to its use in infrastructure applications, which are mostly in aggressive environments, such as harsh marine environments with highly possible chloride-induced corrosion. Valipour etal.  reported that natural zeolite from a durability point of view in harsh marine environments could be a good option for replacement of cement even comparing with metakaolin and silica fume, which would be beneficial even from environmentally friendly point of view. Because concrete containing 20% replacement level in splash exposure showed chloride diffusion resistance even better than metakaolin with 5% replacement level and silica fume with 5 and 7.5% replacement level.
Several studies have indicated that lowering the w/b ratio and adding different types of pozzolanic materials to the mix can improve the compressive strength, durability, and permeability of concrete. Lowering the w/b ratio reduces the porosity, which thereby reduces chloride ingress during the exposure period by as much as 25% . Moreover, pozzolanic materials are being used widely as mineral admixtures to enhance the mechanical properties of concrete and thereby improve the concretes microstructure. These admixtures, either natural or artificial, reduce the Ca(OH)2 content produced during the cement hydration process and instead form CSH gel through the secondary reactions. This process retards the hydration process, significantly reducing the porosity and permeability of the concrete [73, 74, 75].
Valipour etal.  found that the partial replacement of cement by 10 and 20% natural zeolite drives a higher compressive strength at 28days, while 30% zeolitic replacement decrease the compressive strength when compared with conventional concrete. Moreover, the use of natural zeolite to improve the durability of concrete in aggressive environments, such as the Persian Gulf, results in a concrete with appreciably low chloride permeability.
Nowadays, there is a discussion concerning the role of natural zeolitic effects on the blended cement hydration during the time. During the early stage of hydration, the effects of zeolite are related to the critical role played by their structure and the large surface area of the particles determining the cation ability in the pore solution and the collateral effect on stimulation of Portland cement hydration due to the low reaction degree of the zeolite . The later stage is the proper pozzolanic reaction between the CH liberated during the hydration of cement and the soluble SiO2 and Al2O3 present in bulk zeolite occur after 2 weeks producing compounds with cementing properties [78, 79]. Some zeolites are thermally activated . zen et al. , Cornejo et al. , and Garca de Lomas et al.  studied the early-age hydration heat of Portland cement blended with a spent zeolite catalyst in an amount of up to 35% of the mass of cement, but the composition of the applied catalysts was significantly different from the natural zeolite. Caputo et al.  analyzed the hydration heat development in natural zeolite samples mixed with portlandite in a 1:1 ratio.
Furthermore, Tydlitt etal.  concluded that natural zeolite did not react during the early age, but it causes the acceleration of cement phases hydration. Hence, the early effects of zeolitic addition depend on their physical and chemical characteristics, and it also depends on the Portland cement composition.
Supplementary cementitious materials (SCMs) are natural or by-product materials, which react with Ca(OH)2, (CH), and form hydraulic compounds, such as hydrated calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) . Natural zeolite belongs to the group of natural SCM, whose pozzolanic activity depends on several factors (chemical and mineralogical composition, particle size distribution, specific surface area, cation-exchange capacity, Si/Al ratio of the zeolite framework, etc.) . Each of these factors provides unique characteristics to each cement mix.
In the previous studies concerning the use of zeolites in concrete production, one of the most frequent topics was their pozzolanic activity as a fundamental condition for their utilization as supplementary cementitious materials (SCMs). Perraki etal.  reported a good pozzolanic reactivity of zeolite, 0.555g of Ca(OH)2 per 1g of zeolite according to the Chapelle test. Ahmadi and Shekarchi  found out that the pozzolanic activity of zeolite was lower than silica fume but higher than fly ash.
Many studies have promoted the use of the zeolite-bearing tuffs as SCMs due to their positive influence on the long-term compressive strength and durability. Nevertheless, the variability in tuffs mineralogical and physical properties results in limited understanding of pozzolanic activity of natural zeolites.
When zeolite is added to the cement, at a level of around 10%, some characteristics are modified, such as, an increase in compressive strength [43, 85], a decrease in pore size [86, 87], and an increase in corrosion resistance to the acid solution [55, 88].
Many authors have talked about the appropriate amount of zeolite that must be incorporated into the cement, so that it improves its properties or it can maintain them. Najimi etal.  found out that incorporation of 15% natural zeolite in the blended binder improved compressive strength of concrete, but for concrete with 30% zeolitic content, they observed a 25% strength decrease even with adding a superplasticizer, which was not used in the reference mix; they concluded that concretes incorporating zeolite are characterized by the reduction in the heat of hydration and consequently of thermal cracking; and they also improved durability properties such as chloride ion penetration, corrosion rate, drying shrinkage, and water penetration. Ahmadi and Shekarchi  also reported that the incorporation of natural zeolite as a mineral admixture in concrete enhanced its durability properties. However, various types, structures, and purities of natural zeolites influence concrete strength and durability in different ways and can lead in some cases to contradictory results in experimental studies and observed an increase in compressive strength for up to 20% of natural zeolite used as Portland cement replacement, but this was achieved with an increasing amount of superplasticizer in the mixes containing zeolites. Uzal and Turanli  reported the similar compressive strength of mortar with 55% zeolite in the binder to that of 100% Portland cement mortar, but once again, this could only be achieved using superplasticizers; they describe that a lime reactivity of the clinoptilolite zeolite is comparable to silica fume, higher than fly ash and a non-zeolitic natural pozzolan. Therefore, calcium hydroxide as a cement hydration product combines with natural zeolite consisting of reactive SiO2 and Al2O3 to form calcium hydrosilicates. Karakurt and Topu  found 30% replacement of Portland cement by zeolite in their blended cement mortars as optimum; the compressive strength was similar to the reference mortar. Valipour etal.  observed a fast decrease in the compressive strength of concrete with the increasing amount of zeolite (1030% of the mass of Portland cement) in the mix, even with an increasing superplasticizer dosage. Investigations of mechanical properties of concretes show that the substitution of cement by zeolite resulted in some reduction in strength until 90days of hardening, but after 180days, compressive strength of concretes containing zeolite exceeds the strength of concrete without zeolite. Introduction of zeolite and chemical admixtures in concrete permits the modifications of the phase composition of cement hydration products with the formation of an extra amount of calcium hydrosilicates, hydrogelenite, and ettringite .
Najimi etal.  concluded that concretes incorporating zeolite are characterized by the reduction of the heat of hydration and consequently of thermal cracking and improved durability properties such as chloride ion penetration, corrosion rate, drying shrinkage, and water penetration. Sabet etal.  and Ahmadi and Shekarchi  also reported that the incorporation of natural zeolite as a mineral admixture in concrete enhanced its durability properties. However, various types, structures, and purities of natural zeolites influence concrete strength and durability in different ways and can lead in some cases to contradictory results in experimental studies.
Uzal and Turanli  reported that the type of major cation was found to be one of the probable factors governing the pozzolanic activity of clinoptilolite zeolites by affecting their degree of solubility in alkaline conditions. Experimentally demonstrated that pastes of blended cements containing a large amount of clinoptilolite tuff contain less amount of pores >50nm when compared with Portland cement paste, which is beneficial in terms of mechanical strength and impermeability of the pastes.
The methods of preparation of cement mixtures with zeolite vary according to the type of study and parameter that is intended to know, and this is due to the constant search to improve their properties. However, there are regulations that help to delimit the use and management of pozzolans, this, if it is intended that the study has a commercial impact, or that meets the standards established for the development of mortars (Table 1).
Several authors have investigated how to improve the mechanical properties of cement with zeolite, and its resistance to compression is specific. Valipour etal.  and Chan  were agreed that, to improve this characteristic, cement mixtures should not exceed 45% of zeolitic addition. While if what is desired is to avoid the carbonation process of the cement, the additions should not exceed 30% [62, 91, 92] because this process is more evident in the early hydration phase, but it reduces with the passage of time. It is necessary to consider that the hydration of the cement is perhaps the most important aspect because it will derive almost all the processes addressed in this article, besides being a determining factor in the cementing process of the mixture. Several researchers [84, 93, 94] concluded that the addition of zeolite to the cement paste greatly increases the early stage of hydration, and therefore, it is not recommended to exceed 40% of pozzolanic addition in the mixture. In this way, operational parameters that contribute to the development of a composite mix with the best features and operational performance can be established.
It is not enough to establish limits in the substitution of cement with pozzolans because the structure of the zeolite also plays a very important role in the interaction with the mixture; as already mentioned, there is a great variety of zeolites, each with its respective family and structure , and the treatment that each one must receive before its incorporation into the cementing pastes can be very different. First, it must be understood that the Si/Al ratio will define the homogeneity of the mixture and the setting process  with a higher percentage of alumina in their structure that will tend to have a weaker and slower setting, while those that have a very large pore diameter will facilitate the carbonation of the mixtures. There are many ways to incorporate zeolite to cement pastes, but they have in common the amorphization of the same, whether, by mechanical, chemical, or thermal methods, the main objective is to generate a correct balance between the Portland cement and the percentage of Si/Al content in the zeolite.
The dealumination is one of the most widespread methods for the control of the percentage Si/Al present in the zeolite and encompasses the aforementioned methods. In 1968, McDaniel and Maher prepared the ultra-stable Y zeolite by combining procedures for the exchange of sodium ions with ammonium and hydrothermal treatments at elevated temperatures (T 600C). Under the conditions of deep bed, these treatments caused the removal of structural Al with the consequent decrease of the cell parameter. On the contrary, when the hydrothermal treatment was carried out in a shallow bed, the protonated form of the zeolite was obtained without causing dealumination. It has been possible to dealuminate up to 98% Y zeolite by hydrothermal treatments without an appreciable loss of crystallinity.
In 1968, Kerr developed a method to dealuminate Y zeolites at low temperature (around 100C) by using a hydrolyzing and complexing agent of aluminum such as EDTA  with this method; however, you cannot dealuminate above 70% without drastic losses of crystallinity.
Finally, Skeels and Breck reported a procedure in which ammonium hexafluorosilicate is used as a deadening agent, under mild conditions at low temperatures. It is a quick and simple method, but the superior level of dealumination, as with EDTA, is limited to 70% to avoid crystalline collapse.
The textural characterization of the zeolite-cement compound consists of measuring the pore size present in the element; the analysis of this porosity has as an objective to measure the surface of the pores and the volume of the same. It should be mentioned that the compound may have microporosity or mesoporosity; as the study by Franus etal. , there are several ways to calculate the volume, distribution, and surface area of the pores among which are the general isotherm equation based on the combination of a modified Kelvin equation and a statistic thickness of the adsorbed film and the multilayer adsorption theory .
The mechanical characterization performed on cement pastes with zeolitic content does not differ from the typical mechanical compression tests (performed to see the maximum load before causing a fracture), which are carried out by means of a universal machine. However, both the size of the specimens and the laboratory conditions (temperature, pressure, and percentage of aggregates) depend on the author and the results that he intends to obtain. There is a lot of research on the mechanical state of the test tubes [41, 51, 99, 101], and it is important to mention that in most of them, the state of operation is evaluated after having been subjected to adverse media, such as chloride attack or exposure to acid media.
At present, due to the many investigations that exist on cement with zeolitic addition, we can find large areas of opportunity for its application. However, its use as a cement for construction is the most researched application [9, 41, 93, 96], and this is obvious when the main function of this compound is to work as an alternative to ordinary cement (usually the Portland type) in the cement industry building. Although there are other applications of the same scope and not so obvious, which have not been given the same attention, among them we can find its use for the stabilization of sandy soils prior to the construction of roads [102, 103], agent for the reduction in pollutants and environmental conditions [76, 104], and its application in cementing operations carried out on the high seas and oil platforms [46, 105].
The partial replacement of cement is a fact that every day becomes more important; it is an activity that is already carried out and that although there are few cement producers that commercialize with these compounds, it is a great step for the reduction in emissions of CO2. Many authors have contributed and are still investigating the properties that this mixture provides us in order to improve them and to be able to develop a mixed cement paste that is capable of equalizing the effectiveness of Portland cement, which although it is close to it, in the case of zeolite as a pozzolan, it has not yet been achieved that this represents 50% of the mixture. Fortunately, with the growing research and development of new methods for the synthesis and management of these minerals, achieving a balance between the costs of production and the effectiveness of the product can be a reality. It should be mentioned that the use of zeolite as a pozzolan is not a whim, and although it competes with other pozzolans that can deliver a better mechanical performance such as silica fume and volcanic ash, the possible production savings due to availability and improvement from other areas such as resistance to carbonation, transport properties, hydration of the mixture, and absorption of contaminants are concepts that are worth investigating and investing for their development and improvement.
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Dublin, July 08, 2021 (GLOBE NEWSWIRE) -- The "North American Concrete Reinforcing Fiber Market 2020-2026" report has been added to ResearchAndMarkets.com's offering. North American concrete reinforcing fiber market is estimated to grow at a CAGR of 4.7% during the forecast period.
Fiber-reinforced concrete can be utilized in several residential applications such as pool construction with shotcrete, driveways, sidewalks, drainage, basements, foundations, colored concrete, and more. It is appropriate for concrete applications that need protection from plastic and drying shrinkage, increased service life, reduced construction costs, improved durability. The fibers application in concrete can decrease the consumption of energy of a construction project and thereby supports green building practices.North American concrete reinforcing fiber market is segmented based on type and application. Based on type, the market is classified into steel fiber, synthetic fiber, natural fiber, glass fiber, and others. Synthetic fibers include polypropylene, polyester, nylon, and polythene.
These fibers are particularly engineered for concrete that is produced from man-made materials to resist in the long-term alkaline concrete environment. Synthetic fibers are extensively added to concrete to minimize plastic shrinkage cracking of structural and reinforced plain concrete and to decrease temperature cracking and shrinkage in structural plain concrete slabs on grade.
Among synthetic fibers that are available in the US, polypropylene is regarded as the most extensively used synthetic fiber in ready mixed concrete. Polypropylene fibers are hydrophobic and therefore, they do not absorb water. Based on application, the market is classified into infrastructure, residential and commercial, and industrial.Some prominent players in the market include Sika AG, BASF SE, Owens Corning, and GCP Applied Technologies Inc. The strategies adopted by the market players to increase their market share include product launches and mergers and acquisitions.
For instance, in May 2018, GCP Applied Technologies Inc. announced the acquisition of UK based R.I.W. Ltd., a provider of waterproofing products. The company offers products for applications in residential and commercial construction.
Key Topics Covered: 1. Report Summary1.1. Research Methods and Tools1.2. Market Breakdown2. Market Overview and Insights2.1. Scope of the Report2.2. Analyst Insight & Current Market Trends2.2.1. Key Findings2.2.2. Recommendations2.2.3. Conclusion3. Competitive Landscape3.1. Company Share Analysis3.2. Key Strategy Analysis3.3. Key Company Analysis3.3.1. Overview3.3.2. Financial Analysis3.3.3. SWOT Analysis3.3.4. Recent Developments4. Market Determinants4.1. Motivators4.2. Restraints4.3. Opportunities5. Market Segmentation5.1. North American Concrete Reinforcing Fiber Market by Type5.1.1. Steel Fiber5.1.2. Synthetic Fiber5.1.3. Natural Fiber5.1.4. Glass Fiber5.1.5. Others5.2. North American Concrete Reinforcing Fiber Market by Application5.2.1. Infrastructure5.2.2. Residential and Commercial5.2.3. Industrial6. Regional Analysis6.1. United States6.2. Canada7. Company Profiles
Shares of SGOCO Group(NASDAQ: SGOC) were up over 500% on Friday on heavy trading volume. The penny stock didn't release any news to trigger this price movement. SGOCO Group is a penny stock that manufactures phase change storage systems, among other items.
"This is speculative but I think you stick with it," responded Jim Cramer. According to the company's website they do "research and product development of pharmaceuticals and biologic agents for the prevention and treatment of human neurological and neurodegenerative disorders, pain and cancer." In the daily bar chart of AVXL, below, we can see that the shares made a base in the second half of 2020 and then started a strong advance in late January and early February.
Shares of Novavax (NASDAQ: NVAX) dropped 12.7% this week as of the market close on Thursday. The primary reason behind this decline appears to be increasing concerns about the rise of coronavirus variants, especially the highly contagious delta variant. This lack of information about the efficacy of Novavax's vaccine against the delta variant seems to be troubling investors to some extent.
Interest rates have dropped to near zero, bond yields have fallen substantially from pre-COVID levels, and a number of traditional dividend paying stocks cut or postponed payments due to the pandemic. This compounding effect, combined with rising inflation, has created an environment that has seen real yields (nominal interest rate minus inflation) at their lowest level since the 1970s, as measured by the U.S. 10 Year Treasury bond. The current inflationary environment is, to put it mildly, less than ideal for yield-focused investors especially retirees.
Strategy Analytics estimates that 5G smartphone shipments could hit 624 million units this year from just 269 million in 2020. There were almost 136 million 5G smartphones shipped in the first quarter of 2021, according to the research firm, and sales are likely to get stronger as the year progresses. As such, now is a good time to load up on key beneficiaries of the growth in 5G smartphones.
The good news: That pension and your savings are and will be great assets for you in retirement, so congratulations on that! There are many factors that go into knowing how much youll need for retirement, and a few ways to break down these annual estimates. For example, if you were to use the 4% rule, which is a traditional rule of thumb that suggests you take out 4% of your retirement savings every year to live on, youd generate about $30,000 to $35,000 a year, said Morgan Hill, chief executive officer of Hill and Hill Financial.
In this article, we will be looking at the 10 best dividend stocks for long term. To skip our detailed analysis of dividend investing, you can go directly to see the 5 Best Dividend Stocks for Long Term. Dividend investing is a strategy that has managed to stick around as long as it has for two 
The stock market put in a strong showing on Friday, sending the S&P 500 (SNPINDEX: ^GSPC) and Nasdaq Composite (NASDAQINDEX: ^IXIC) to new record levels. Earlier this year, the investing thesis for many fast-growing companies got called into question by changing macroeconomic conditions. For many investors, Snowflake has been a colossal disappointment.
In our June 7 review of Apple we wrote that "Traders who are not already long AAPL could go long AAPL at current levels risking to $116. The $169 area is our first upside price target." Prices have broken out to a new 52-week high today so let's take a quick look at the charts again.
While the stocks that pay dividends generally do so on a quarterly basis, there is a select group of companies that pay them out monthly. Here are two REITs that income investors might appreciate knowing about, that pay monthly dividends, and that have above-market yields. Realty Income (NYSE: O) is a Dividend Aristocrat that calls itself The Monthly Dividend Company.
In this article, we discuss the 20 Chinese companies listed on NYSE/NASDAQ/AMEX. If you want to skip our detailed analysis of these companies, go directly to the 5 Chinese Companies Listed on NYSE/NASDAQ/AMEX. The trade tension between the United States and China over the past few years has dominated headlines around the world, fueling speculation 
A beam resting on supports at each end trends to bend under its own weight and under applied loading. This causes compression along the top part of the beam and tension along the bottom part. In other words, there is a tendency for the bottom of the beam to stretch.
Concrete is strong in compression, but weak in tension, and for this reason, a plain concrete beam has little strength. The tensile weakness of concrete is overcome by casting steel bars into the sections where tension is likely to occur. When a load is applied on beam, cracks still occur in the concrete, but the tension is carried by the steel reinforcement.
The principle of prestressing is to compress the beam before it is loaded in such a way that stresses are induced in the section which is opposite in action to those arising under loading. Thus the bottom of the beam is compressed by the prestressing so that tension arising when it is loaded will be entirely neutralized.
Furthermore, the compression in the concrete is also of great importance in resisting shear. If one imagines a prestressed beam as a row of blocks pressed together, it is easy to see that if they are pressed together sufficiently tightly they will not fall out when a load is applied. This condition aided by the device of sweeping cables upwards at the end of the beam will usually eliminate the need for steel reinforcement to resist shear stresses.
Since the size of prestressed members is less than that of the conventional reinforced concrete members, the dead load of the structure is often reduced sufficiently, hence savings of materials in structural members.
The use of prestressed concrete as a structural medium for bridge construction has been gaining popularity. With the increase in transportation, the requirement for bridges became acute and the shortage of general building materials gave an impetus to use of prestressed concrete in all civil engineering activities.
The development of prestressed concrete technology over the last two decades can be attributed to the research, development, improvement and advancement of materials, technology and construction techniques. The existing materials used in construction were better utilized and their properties enhanced, new materials developed to suit the special needs of prestressed concrete. The development in technology also seen in the concept of form-work and analytical techniques.
Prestressed Concrete Piles: Prestressed concrete piles have been used extensively in the construction of buildings and marine structures. Due to its high strength for handling and a high degree of durability in seawater and other adverse environments, the use of prestressed concrete piles became very popular in the construction of marine structures. The prestressed concrete piles have many advantages in comparison with conventional piles - a few of them are:
In view of the above advantages, the prestressed concrete pile is an ideal choice for deep foundations with heavy loading on weak soil. At present, prestressed concrete piles are being used as sheet piles, fender piles and soldier piles. It also used for carrying vertical loads with different soil strengths and found to be durable in varied environments ranging from sub-arctic to the desert.
Rock /soil Anchors:Prestressing techniques are now used for strengthening an existing structure by anchoring it to the rock or soil. In places where rocks are not available immediately below the ground level, rock-anchors are used to anchor the pile to the rocks that are situated at very large depth. The use of prestressed anchors avoids the driving of the pile all the way to the rock which is available at very large depth. The pile is driven only to a certain depth, depending on the soil condition and prestressed cable is sent through the pile to the rock. The cable is then stressed and grouted.
a. Simply Supported Bridges: They are adopted for medium and short spans. The cross-sections of these beams maybe I, T, two T's or Box shape.The girders can be pre or post-tensioned. These beams may be precast or cast-in-situ and are usually supported by neoprene or other types of bearings at either end.
b. Cantilever Bridges: This method is usually adopted for longer span bridges. In this method, there will be cantilevers extending from each of the piers. There will be a suspended span of the shorter length to connect the cantilevers. The cantilevers are usually extended by anchoring precast segments of short length. Each segment is anchored to the balancing extension on the other side of the pier.
c. Cable-Stayed Bridges:Extremely long spans constructed by using this method of construction. In this type of construction, the deck or slab is held by a number of prestressed cables anchored to the anchor tower. Using this method spans up to 300 m can be constructed.
Prestressed concrete has gained acceptance in the field of marine structures due to its durability, strength and economy. Its application to foundations has already been discussed in the earlier section. Prestressed concrete is now being applied increasingly in the super-structures of the marine projects. A few types of marine structures where prestressed concrete has been adopted are:
It is a well-known fact that marine construction has many problems of its own in its construction procedures. The difficulty at the site especially for the movement of materials and workers, makes quality control a difficult exercise.
Further, highly skilled labour is required in such projects. Such labour is either not available or available at a very high cost. All such factors show that precasting is an ideal choice for marine structure. In precasting, the efficiency and economy can be increased by means of prestressing, especially by pre-tensioning. The pre-tensioned materials can then be made to act monolithically by post-tensioning them subsequently.
a. Aqueducts: Prestressed concrete is found to be the ideal choice for the construction of aqueducts due to its water tightness and crack-free surface. Prestressed concrete, due to its high strength, enables the construction of long-span aqueducts with high water carrying capacity.
b. Water Tanks: Circular water tanks are also constructed by using prestressed concrete. They withstand higher circumferential stress than R.C.C. The wall thickness of the prestressed concrete tanks is much less than that of R.C.C because of its high strength. With these advantages, the use of prestressed concrete for the construction of overhead water tank and reservoirs is gaining popularity.
Application of prestressed concrete in the field of construction of industrial structures is getting momentum. The tie members of the trusses are usually prestressed. The advantages of using prestressed concrete are:
In the field of pretension, much progress has made to great advantage. The extensive manufacture of prestressed electric transmission poles is just one of the many application of pretension. The recent and important addition in the list is the railway sleeper. A number of plants manufacturing these sleepers springing up in every corner of the world. Precast pre tensioned members are also used extensively for prefabricated houses.
In this atomic age, the concept of prestressed concrete lives up to its reputation as the technology that can offer solutions even to the most difficult and intricate problems faced by the civil engineering industry. The designers of the reactors have realized the advantages of prestressed concrete and are now designing their pressure-vessels and container-vessels of the reactors, recommending the use of prestressed concrete.