EARLY STRENGTH FOR IMMEDIATE NEEDS Portland Type III cement is a high early strength cement that is commonly used in building applications where compressive strength must be maximized during the first 24 hours. This includes structures such as bridges, buildings, and footbridges.
Type III cement has higher calcium aluminate content than Types I or II cement. This makes it more reactive with water and more prone to forming ettringite. Ettringite is a crystalline solid composed of magnesium and hexagonal crystals of aluminum phosphate tetrahedron. It forms when water reacts with calcium hydroxide from any source (including that produced by Type I or II cements) to form a protective coating on the concrete surface. The ettringite then acts as a filler material that increases the concrete's compressive strength.
Types I and II cements contain less calcium aluminate than Type III cement. As a result, they tend to form less ettringite and have longer setting times. This allows them to be used in situations where quick strength is not necessary. For example, they are commonly used as a base cement for asphalt pavement or playground surfaces.
Type IV cement is used in low-strength applications where neither compressive strength nor flexural strength is needed immediately after placement. Examples include driveway sealers and patching compounds.
It is typically utilized in precast concrete manufacture, where its excellent one-day strength allows for rapid mold rotation. It may also be utilized for emergency repairs, as well as the building of machine bases and gate installations. The low heat of hydration of Type IV Portland cement is well recognized. This type of cement can be easily worked while still wet.
Other applications include: driveway anchors, fence posts, pool decking, and playground equipment. Cement is also used in soil stabilization techniques called terracing or hill farming.
Cements are materials that when mixed with water form a solid substance. Cements are classified according to their source of alkaline material, such as limestone or dolomite, which react with carbon dioxide from the air to produce calcium carbonate (the main ingredient in concrete). Cements are further divided into ordinary cements and high-strength cements.
High-strength cements are used in applications where maximum performance is required from the concrete. These applications include structural members inside buildings, bridges, and other concrete products. High-strength cements are also used in large projects like skyscrapers and nuclear power plants that require concrete with very high compressive strengths.
Ordinary cements are used in applications where moderate strength is sufficient. These applications include most residential and commercial construction, including footings, walls, and floors.
Type III high-early strength cement (see Table 1), high cement content (600–1000 lb/cu yd), and lower water-cement ratios are typically used to achieve high early strength concrete (2500–3500 psi compressive in 24 hours). Type III cements are a class of hydraulic cements developed for use in high-strength applications. They contain low levels of silica (<20%) and alumina (<10%), and high levels of calcium oxide (>75%).
Type IV high-early strength cement (see Table 1), similar to type III but with higher calcium oxide content (>85%), is used when even higher early strengths are needed. Type IV cements are available as normal-burned or chemically burned cements.
High-range water-reducing admixtures can be used to reduce the amount of water required for these cements. Low-range water-reducing admixtures can be used to increase the amount of water retained in the concrete for reduced drying times and increased frost resistance.
Type I cements (see Table 1) are used for ordinary concrete that needs to resist compression after 28 days. These cements have high sodium oxide contents (15% or more) that produce low pH values (less than 12) that prevent calcium hydroxide from forming in the concrete before it has time to cure.
Portland Type I/II cement is a general-purpose cement that is commonly used in general construction applications such as precast concrete products, reinforced structures, floors, sewers, bridges, and pavements. It has a maximum heat of hydration of 1250 degrees Fahrenheit and a minimum of 1180 degrees Fahrenheit.
Type I cements are the most common cements used worldwide. They are characterized by high calcium ratios (60% or more) and low alkali ratios (less than 2%). The main mineral components of Type I cements are tricalcium silicate, dicalcium silicate, and alumina. Tricalcium aluminate serves as a solid solution for enhancing flexural strength and durability. Type II cements have higher alkali ratios (3% or more) and can be either acid-resistant or neutralized. Their main mineral component is alite, which is an aluminum-rich tetrahedral clay mineral. Type II cements are used when acid resistance is required.
The fineness of cement particles affects the rate at which they harden and mature. Coarse-grained cements take longer to harden than fine-grained ones because there are more surface areas that need to be covered by water before the cement matrix is formed.