Basics

Q: What is cement?
A: Cement is a fine, soft, powdery substance, made from a mixture of elements found in natural materials such as limestone, clay, sand and/or shale. When cement is mixed with water, it can bind sand and gravel into a hard, solid mass called concrete. Cement is usually grey. White cement is also available, but is usually more expensive. 
1. Cement mixed with water, sand and gravel, forms concrete. 
2. Cement mixed with water and sand, forms cement plaster. 
3. Cement mixed with water, lime and sand, forms mortar. 
Cement powder is extremely fine; one kilo (2.2lbs) contains over 300 billion grains. The powder is so fine it will pass through a sieve capable of holding water.
In India, Ordinary Portland Cement (OPC) is manufactured in three grades, viz. 33 grade, 43 grade and 53 grade. The numbers indicate the compressive strength obtained after 28 days, when tested as per the stipulated procedure.
Apart from OPC, there are several other types of cement, mostly meant for special purposes, e.g. sulphate resistant cement, coloured cement, oil well cement etc. However, there are some general-purpose cement, the commonest one being Portland Pozzolana Cement (PPC).

Q: What are Type I/II or Type II/V cements?
A: Type I/II and Type II/V cements simply means that the cement complies with the requirements of ASTM C 150, Standard Specification for Portland Cement. It is quite common to find cements that comply with multiple cement designations such as Type I/II and Type II/V.

Q. Is there any shelf life of cement? 
A: Cement is a hygroscopic material, meaning that in presence of moisture it undergoes chemical reaction termed as hydration. Therefore cement remains in good condition as long as it does not come in contact with moisture. If cement is more than three months old then it should be tested for its strength before being employed.

What is natural cement?
Natural cement is obtained by burning an argillaceous or a magnesian limestone, which happens to have the proper chemical composition. The resulting clinker is then finely ground and is at once ready for use. Such cement was formerly and is still commonly called Rosendale cement, owing to its having been produced first in Rosendale, Ulster County, New York.  The strength and uniformity of natural cements are lower than those of Portland cements; but these are more historically accurate materials for restoration projects, which is their primary application. Natural cements were extensively used in 19th and early 20th century construction in several historic structures. However, with improved technology for producing Portland cements, sales of natural cements began to decline in the late 1800s, stopping entirely by the mid 1970s.

Q: How is cement made?

 1) Limestone, the major ingredient needed for making cement is quarried. Small quantities of sand and clay are required as well. Limestone, sand and clay contain the four essential elements required to make cement: calcium, silicon, aluminium and iron. 

2) Boulder-size limestone rocks are transported from the quarry to the cement plant and fed into a crusher, which crushes the boulders into marble-size pieces. 

3) The limestone pieces then go through a blender where they are mixed with the other raw materials in the right proportion.  

4) Raw materials are then ground to a powder. This is sometimes done with rollers that crush the materials against a rotating platform. 

5) This mixture then goes into a huge, extremely hot, rotating furnace to undergo a process called ‘sintering’. Sintering means: to cause to become a coherent mass by heating without melting. In other words, the raw materials become partially molten. The raw materials reach about 2700° F (1480°C) inside the furnace. This causes chemical and physical changes to the raw materials and they come out of the furnace as large, glassy, red-hot cinders called ‘clinker’. 

6) This clinker is cooled and ground into a fine grey powder. A small amount of gypsum is added during the final grinding. The finished product is Portland cement. 

The cement is then stored in silos (large holding tanks) where it awaits distribution. 
The cement is usually shipped in bulk in purpose-made trucks, by rail or even by barges and ships. Some is bagged for those who want small quantities.

Q. What are the different types of cement?
There are many varieties in cement, following are the different types of cement with their characteristics and the areas they are most required.

• Portland Blast Furnace slag cement (PBFSC):The rate of hydration heat is found lower in this cement type in comparison to PPC. It is most useful in massive construction projects, for example - dams.
• Sulphate Resisting Portland Cement: This cement is beneficial in the areas where concrete has an exposure to seacoast or sea water or soil or ground water. Under any such instances, the concrete is vulnerable to sulphates attack in large amounts and can cause damage to the structure. Hence, by using this cement one can reduce the impact of damage to the structure. This cement has high demand in India.
• Rapid Hardening Portland Cement: The texture of this cement type is quite similar to that of OPC. But, it is bit more fine than OPC and possesses immense compressible strength, which makes casting work easy.
• Ordinary Portland Cement (OPC): Also referred to as grey cement or OPC, it is of much use in ordinary concrete construction. In the production of this type of cement in India, Iron (Fe2O3), Magnesium (MgO), Silica (SiO2), Alumina (AL2O3), and Sulphur trioxide (SO3) components are used.
• Portland Pozolona Cement (PPC): As it prevents cracks, it is useful in the casting work of huge volumes of concrete. The rate of hydration heat is lower in this cement type. Fly ash, coal waste or burnt clay is used in the production of this category of cement. It can be availed at low cost in comparison to OPC.
• Oil Well Cement: Made of iron, coke, limestone and iron scrap, Oil Well Cement is used in constructing or fixing oil wells. This is applied on both the off-shore and on-shore of the wells.
• Clinker Cement: Produced at the temperature of about 1400 to1450 degree Celsius, clinker cement is needed in the construction work of complexes, houses and bridges. The ingredients for this cement comprise iron, quartz, clay, limestone and bauxite.
• White cement: It is a kind of Ordinary Portland Cement. The ingredients of this cement are inclusive of clinker, fuel oil and iron oxide. The content of iron oxide is maintained below 0.4% to secure whiteness. White cement is largely used to increase the aesthetic value of a construction. It is preferred for tiles and flooring works. This cement costs more than grey cement.

Apart from these, some of the other types of cement that are available in India can be classified as:

• Low heat cement
• High early strength cement
• Hydrophobic cement
• High aluminium cement
• Masonry cement

Q: How is Portland cement made?
A: Materials that contain appropriate amounts of calcium compounds like silica, alumina and iron oxide are crushed, screened and placed in a rotating cement kiln. Ingredients used in this process are typically materials such as limestone, marl, shale, iron ore, clay and fly ash.
The kiln resembles a large horizontal pipe with a diameter of 10–15ft (3–4.1m) and a length of 300ft (90m) or more. One end is raised slightly and the raw mix is placed in the high end; as the kiln rotates, the materials move slowly toward the lower end. Flame jets are at the lower end and all the materials in the kiln are heated to high temperatures that range between 2700 and 3000°F (1480 and 1650°C). This high heat drives off, or calcines, the chemically combined water and carbon dioxide from the raw materials and forms new compounds (tricalcium silicate, dicalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite). For each ton of material that goes into the feed end of the kiln, two thirds of a ton of clinker comes out the discharge end. This clinker is in the form of marble sized pellets. The clinker is very finely ground to produce Portland cement. A small amount of gypsum is added during the grinding process to control the cement’s set or rate of hardening.

Q: Are there different types of Portland cement? 
A: Though all Portland cement is basically the same, eight types of cement are manufactured to meet different physical and chemical requirements for specific applications: 
Type I is a general purpose Portland cement suitable for most uses. 
Type II is used for structures in water or soil containing moderate amounts of sulphate, or when heat build-up is a concern. 
Type III cement provides high strength at an early state, usually in a week or less. 
Type IV moderates heat generated by hydration that is used for massive concrete structures such as dams. 
Type V cement resists chemical attacks by soil and water high in sulphates. 
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. 
White Portland cement is made from raw materials containing little or no iron or manganese.

Q: What is Fibre Reinforced Concrete? 
A: Low Fibre volume composite concrete contains less than 1% fibre. It is used for field applications involving large volumes of concrete. The fibres do not significantly increase the strength of the concrete. Low fibre volume concrete is used for paving roads. 
High Fibre Volume Concrete: Typically used for thin sheets with cement mortar mix. The fibre volume in this mix ranges from 5% to 15%. 
High Fibre Volume Composite: The fibre volume in this mix can be as high as 40%. This significantly increases the strength and toughness of the mix. The reinforcement in High Fibre Volume Composite concrete is usually in sheet form. This reinforced concrete type is used in roof and wall panels.
 
Q: What is the difference between cement and concrete?
A: Concrete should not be confused with cement because the term cement refers only to the dry powder substance used to bind the aggregate materials of concrete. Upon the addition of water and/or additives the cement mixture is referred to as concrete, especially if aggregates have been added.

Q: What is concrete? 
A: Concrete is a mixture of cement, water, sand and gravel (stones, crushed rock). The mixture eventually hardens into a stone-like material. Cement and water are the two ingredients that chemically react; the gravel and sand give strength. 
 
Q. How was concrete made in the earlier times?
A: During the Roman Empire, Roman concrete (or Opus caementicium) was made from quicklime, pozzolanic ash/pozzolana and an aggregate of pumice. Its widespread use in many Roman structures, a key event in the history of architecture termed the Concrete Revolution, freed Roman construction from the restrictions of stone and brick material and allowed for revolutionary new designs both, in terms of structural complexity and dimension. Concrete, as the Romans knew it, was in effect a new and revolutionary material. Laid in the shape of arches, vaults and domes, it quickly hardened into a rigid mass, free from many of the internal thrusts and strains, which troubled the builders of similar structures in stone or brick.

Q: How is modern structural concrete different from the earlier form of concrete?
A: Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand layering together with the placement of aggregate, which in Roman practice often consisted of rubble. Second, integral reinforcing steel gives modern concrete assemblies great tensile strength, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.

Q: What does ‘curing’ concrete mean? 
A: Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only in the presence of water and if the concrete’s temperature stays within a suitable range. During the curing period-from, five to seven days after placement for conventional concrete, the concrete surface needs to be kept moist to permit the hydration process. New concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.

Q: What is Reinforced concrete? 
A: Reinforced concrete contains steel reinforcing that is designed and placed in structural members at specific positions to cater for the stress conditions that the member is required to accommodate.

Q. What is Prestressed concrete? 
A: The principle behind Prestressed concrete is that compressive stresses induced by high-strength steel tendons in a concrete member before loads are applied will balance the tensile stresses imposed in the member during service. 
For example a horizontal beam will tend to sag down. However, if the reinforcement along the bottom of the beam is prestressed, it can counteract this.
In pre-tensioned concrete, prestressing is achieved by using steel or polymer tendons or bars that are subjected to a tensile force prior to casting; and for post-tensioned concrete, after casting.

Q. What are the sought after properties of concrete?
A. 1. The concrete mix is extremely workable. It can be placed and consolidated properly. 

2. Desired qualities of the hardened concrete are met. For example, resistance to freezing and thawing and deicing chemicals, watertightness (low permeability), wear resistance and strength. 

3. Economy. Since the quality depends mainly on the water to cement ratio, the water requirement should be minimised to reduce the cement requirement (and thus reduce the cost).
The following steps reduce water and cement requirements:
Use the stiffest mix possible 
Use the largest size aggregate practical for the job
Use the optimum ratio of fine to coarse aggregate

Q: What is the composition of Concrete 
A: 11% Cement (usually Portland) 
16% Water 
6% Air 
26% Sand 
41% Gravel or crushed stone

Q: Descriptive composition of Concrete.
A: There are many types of concrete available, created by varying the proportions of its main ingredients.
The mix design depends on the type of structure being built, how the concrete will be mixed, delivered and how it will be placed to form the structure.

Q: How is white cement different and why is it used in decorative concrete? 
A: There are only slight chemical and physical differences between grey Portland cement and white Portland cement. This is due to raw material differences and sometimes, though not always, slight differences in manufacturing. White cement has small amounts of the oxides (particularly iron and manganese) that impart the greyish colour normally associated with Portland cement.

Q. What are the decorative finishes that can be applied to concrete surfaces? 
A: Adding pigment before or after the concrete is placed and using white cement rather than conventional grey cement, using chemical stains or exposing colourful aggregates at the surface may add colour to concrete. Textured finishes can vary from a smooth polish to the roughness of gravel.
Geometric patterns can be scored, stamped, rolled, or inlaid into the concrete to resemble stone, brick or tile paving. Other interesting patterns are obtained by using divider strips (commonly redwood) to form panels of various sizes and shapes rectangular, square, circular or diamond.
Special techniques are available to make concrete slip-resistant and sparkling.

Q: What are the different forms of sulphate in Portland cement and how can we analyse cement for SO3?
A: Sulphates in Portland cement can be broadly categorised as:
1.  Added sulphates – gypsum, hemihydrates, anhydrite, several synthetic forms of sulphates (typically by-products like flue gas desulphurisation materials). Clinker sulphates include arcanite, aphthitalite, calcium langbeinite and thenardite. Although normally reported as SO3 (% by mass) for consistency, sulphur can be found in any combination of forms. Elemental sulphur is almost never found in Portland cement, except in trace amounts.
Added sulphates are blended with clinker during the final grinding of the cement, in amounts needed to control early setting properties as well as shrinkage and strength development. The amount needed varies depending on the chemistry and fineness of the cement, but is typically on the order of 5% by mass. The most common form of sulphate added to Portland cement is gypsum, some of which is intentionally dehydrated by the heat of grinding to form hemihydrates, which are more soluble and therefore available to control early hydration reactions.
Clinker sulphates form naturally during clinker production. These sulphates tend to volatilise at the temperatures of cement kilns (up to about 1450ºC) and condense on the outer surface of clinker nodules as alkali sulphates, during the last stage of clinker production (rapid cooling). Again, the amount depends on the chemistry of the raw materials and kiln operating conditions, making the cement somewhat unique. These alkali sulphates also are soluble enough to help control early hydration reactions. Some clinker sulphate is also incorporated into other cement phases.

Since cement is unique, chemical analyses are the best method of determining the SO3 content of cements. Typically the total SO3 content is measured (or elemental S measured and converted to SO3) through methods in ASTM C 114 (or AASHTO T 105). XRF analysis is probably the most common technique.

Q: What is air-entrained concrete? 
A: Air-entrained concrete contains billions of microscopic air cells per cubic foot. These air pockets relieve the internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes. Air-entrained concrete is produced through the use of air-entraining Portland cement, or by the introduction of air-entraining agents, under careful engineering supervision. The amount of entrained air is usually between 4% and 7% of the volume of the concrete, but may be varied as required by special conditions.

Q: What are recommended mix proportions for good concrete? 
A: Good concrete can be obtained by using a wide variety of mix proportions if proper mix design procedures are used. The general custom is the rule of 6’s: 
A minimum cement content of 6 bags per cubic yard of concrete 
A maximum water content of 6 gallons per bag of cement 
A curing period (keeping concrete moist) a minimum of 6 days 
An air content of 6% (if concrete will be subject to freezing and thawing)

Q: Will concrete harden under water? 
A: Portland cement is a hydraulic cement, which means that it sets and hardens due to a chemical reaction with water. Consequently, it will harden under water.

Q: What does 28 -day strength mean? 
A: Concrete hardens and gains strength as it hydrates. The hydration process continues over a long period of time; beginning rapidly and progressively slowing down. To measure the ultimate strength of concrete would require a wait of several years. This would be impractical, so a time period of 28 days was selected, by specification writing authorities, as the age that all concrete should be tested. At this age, a substantial percentage of the hydration has taken place.

Q: What is 3,000 pound concrete? 
A: Concrete that is strong enough to carry a compressive stress of 3,000psi (20.7MPa) at 28 days is 3,000 pound concrete. Concrete may be specified at other strengths as well. Conventional concrete has strengths of 7,000psi or less; concrete with strengths between 7,000 and 14,500psi is considered high-strength concrete.

Q: How do you control the strength of concrete? 
A: The easiest way to add strength is to add cement. The factor that most predominantly influences concrete strength is the water to cement ratio in the cement paste that binds the aggregates together. The higher this ratio is, the weaker the concrete will be and vice versa. Every desirable physical property will be adversely affected by adding more water.

Q: What is alkali-silica reactivity (ASR)? 
A: Alkali-silica reactivity is an expansive reaction between reactive forms of silica in aggregates and potassium and sodium alkalis, mostly from cement, but also from aggregates, pozzolans, admixtures and mixing water. External sources of alkali from soil, deicers and industrial processes can also contribute to ASR. The reaction forms an alkali-silica gel that swells as it draws water from the surrounding cement paste, thereby inducing pressure, expansion and cracking of the aggregate and surrounding paste. This often results in map-pattern cracks, sometimes referred to as alligator pattern cracking. ASR can be avoided through

• Proper aggregate selection
• Use of blended cements
• Use of proper pozzolanic materials
• Contaminant-free mixing water

Q. What are Supplementary Cementations Materials (SCM)? 
A: Supplementary Cementations Materials (SCM) like silica fumes, meta-kaolin, fly ash, slag are the substances which improve the properties of concrete and enhance its durability, by reducing pore size in concrete through better particle distribution and through increased packing density of the concrete.

Q. How fineness of cement affects strength gain? 
A: Finer cement particles imply more particles in unit weight. This enhances the reaction rate, which in turn will result in faster gain of strength at earlier stages.

Q: Why do concrete surfaces flake and spall? 
A: Concrete surfaces can flake or spall for one or more of the following reasons:
In areas subjected to freezing and thawing, the concrete should be air-entrained to resist flaking and scaling of the surface. If air-entrained concrete is not used, there will be subsequent damage to the surface.
The water/cement ratio should be as low as possible to improve durability of the surface. Too much water in the mix will produce a weaker, less durable concrete, in turn leading to early flaking and spalling of the surface.
The finishing operations should not begin until the water sheen on the surface is gone and excess bleed water on the surface has had a chance to evaporate. If this excess water is worked into the concrete because the finishing operations are begun too soon, the concrete on the surface will have too high a water content and will be weaker and less durable 

Q: How do you remove stains from concrete? 
A: Stains can be removed from concrete with dry or mechanical methods, or by wet methods using chemicals or water.
Common dry methods include sandblasting, flame cleaning, shotblasting, grinding, scabbing, planning and scouring. Steel-wire brushes should be used with care because they can leave metal particles on the surface that later rust and stain the concrete.
Wet methods involve the application of water or specific chemicals according to the nature of the stain. The chemical treatment either dissolves the staining substance so it can be blotted up from the surface of the concrete or bleaches the staining substance so it will not show.
To remove bloodstains, for example, wet the stains with water and cover them with a layer of sodium peroxide powder. Let stand for a few minutes, rinse with water and scrub vigorously. Follow with an application of a 5% solution of vinegar to neutralise any remaining sodium peroxide.

Q: What is Self-Consolidating concrete (SCC)? 
A: SCC is a high-performance concrete that can flow easily into tight and constricted spaces without segregating and without requiring vibration. The key to creating SCC, also referred to as self-compacting, self-levelling, or self-placing concrete, is a mixture that is fluid, but also stable to prevent segregation. 
To achieve the desired flowability a new generation of superplasticisers based on polycarboxylate ethers works best. Developed in the 1990s, they produce better water reduction and slower slump loss than traditional superplasticisers. The required level of fluidity is greatly influenced by the particular application under consideration. Obviously the most congested structural members demand the highest fluidity. However, element shape, desired surface finish, and travel distance can also determine the required fluidity. 
Generally, the higher the required flowability of the SCC mix, the higher the amount of fine material needed to produce a stable mixture. However, in some cases, a viscosity-modifying admixture (VMA) can be used instead of, or in combination with, an increased fine content to stabilize the concrete mixture.

Q: The size of concrete cube is 150mm x 150mm x 150mm as per Indian Standards. Why? 
A: Because the shape effect is the least for the 15cm cube and we get a fairly accurate idea of the strength of the concrete as such.

Q: How do you protect a concrete surface from aggressive materials like acids? 
A: Many materials have no effect on concrete. However, there are some aggressive materials, such as most acids, that can have a deteriorating effect on concrete. The first line of defence against chemical attack is to use quality concrete with maximum chemical resistance, followed by the application of protective treatments to keep corrosive substances from contacting the concrete. Principles and practices that improve the chemical resistance of concrete include using a low water-cement ratio, selecting a suitable cement type (such as sulphate-resistant cement to prevent sulphate attacks), using suitable aggregates, water- and air-entrainment. A large number of chemical formulations are available as sealers and coatings to protect concrete from a variety of environments; detailed recommendations should be requested from manufacturers, formulators or material suppliers.

Q: Why does concrete crack?
A;Concrete, by nature, shrinks as it hardens. When concrete is placed on supporting soil or around steel reinforcement, the concrete mass is prevented from shrinking. This restraint creates internal forces exceeding the strength of concrete; cracks form to relieve these forces.

Q: Does the presence of cracks indicate a structural problem?
A: In most instances, the answer is no. Very narrow ‘hairline’ cracks are aesthetic in nature and do not indicate any structural problem. Cracks that have movement, i.e. where one side of the crack moves relative to the opposite side, should be investigated by a professional engineer.

Q: Why does concrete harden?
A: Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material.

Q: What is concrete used for?
A: Concrete is used to make pavements, pipe, architectural structures, foundations, motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for gates, fences and poles.
Concrete is used more than any other man-made material in the world. As of 2006, about 7.5km3 of concrete is made each year—more than 1m3 for every person on earth.

Q: What are the more popular types of concrete in use?
A: Reinforced concrete and prestressed concrete are the most widely used modern kinds of functional concrete extensions.

Q: What evidence is there for the long life of concrete? 
A: The widespread use of concrete in many Roman structures has ensured that many of them have survived. The Baths of Caracalla is just one example of the longevity of concrete, which allowed the Romans to build this and similar structures across their Empire. Many Roman aqueducts and Roman bridges have masonry cladding to a concrete core, a technique they used in structures such as the Pantheon, the dome of which is concrete.

Q: Who discovered concrete?
A: The Romans used concrete in their structures but the secret had been lost for 13 centuries until 1756, when the British engineer John Smeaton pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate. Portland cement was first used in concrete in the early 1840s. This version of history has been challenged however, as the Canal du Midi was constructed using concrete in 1670. 

Q: What is the role of water in concrete mix? 
A: Combining water with cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it and allows it to flow more easily.
Less water in the cement paste will yield a stronger, more durable concrete; more water will give an easier-flowing concrete with a higher slump. 
Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.
Hydration involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bind the individual sand and gravel particles with other components of the concrete, to form a solid mass.

Q: How do aggregates affect the strength of concrete? 
A: Concrete has a high compressive strength, as the aggregate efficiently carries the compression load. However, it is weak in tension as the cement holding the aggregate in place can crack, allowing the structure to fail. Reinforced concrete solves these problems by adding either metal reinforcing bars, steel fibres, glass fibre or plastic fibre to carry tensile loads.

Q. What are the reasons for slow or fast setting of concrete or mortar?
A: the rate of setting normally depends on the nature of the cement. It could also be due to extraneous factors not related to the cement. Ambient conditions also play an important role. In hot weather, concrete sets faster, whereas in cold weather, setting is delayed. Some salts, chemicals, clay etc., if inadvertently mixed with the sand, aggregate and water could accelerate or delay the setting of concrete.

Q: What do grade numbers indicate? 
A: The grade number indicates the minimum compressive strength of cement sand mortar in N/mm2 at 28 days.

Q. What is slag?
A: Slag is a non-metallic product, essentially consisting glass containing silicates, alumino-silicates of lime and other bases, and is obtained as a by-product in the manufacture of pig iron in blast or electric furnaces. Granulated slag is used in the manufacture of Portland Slag Cement (PSC).

Q. How is PSC made?
A: PSC is made by intergrading clinker, granulated blast furnace slag and gypsum or by blending ground slag with Portland cement.

Q. Where can PSC be used?
A: Slag cement can be used for all plain and reinforced concrete constructions and mass concreting structures such as dams, reservoirs, swimming pools, river embankments, bridge piers etc. It is used with advantage where low heat of hydration and resistance to alkali-silica reactions are desired; for structures in aggressive environments where chemical and mildly acidic waters are encountered (where the use of OPC is not recommended) and for marine constructions, dykes, wharves, etc where sulphuric water is encountered. In short, PSC can be used wherever OPC is used.