by Introduction to Specialty Cement
Ordinary Portland cement is the most commonly used type of cement for construction activities but it does not fulfil all construction requirements. At times, specific properties are required from cement depending upon the application and environment. This is where specialty cements come into play. Specialty Cement are developed to serve unique purposes and meet precise performance standards. They address applications where ordinary cement is not suitable or where enhanced characteristics are required.
Fly-Ash Blended Cement
Fly ash is a by-product of coal combustion in thermal power plants. When mixed with ordinary Portland cement at certain percentages, it enhances some properties of the resulting blended cement. Fly ash blended cement contains 15-35% of fly ash. It has lower heat of hydration compared to pure Portland cement. This makes it suitable for mass concrete works like dams, runways etc where generation of less heat is beneficial. It also increases sulfate resistance and reduces permeability. Due to the pozzolanic nature of fly ash, the blended cement gains strength at a relatively slower pace but attains high strengths over time equivalent to Portland cement.
Specialty Cement White Cement
White cement has applications where aesthetic appearance and light colour are important factors. It contains very low amounts of iron which allows it to retain its whiteness even after hardening. Being free of colouring oxides, white cement is used for decorative concrete works, precast elements, tiles etc. It is also used for repair works so that the patch does not stand out. White cement provides a clean, uniform appearance suitable for high-end construction and architectural applications.
Oil Well Cement
Cements used for oil well cementing operations have to endure very high temperatures, pressures and corrosive environments. Oil well cement must form a strong, impermeable seal between casing and borehole to prevent migration of fluids between geological formations. It requires rapid setting and high early strength development. Special additives provide oil well cement with properties like high compressive strength, low permeability, flame resistance and thermal shock resistance. Proper bonding, zonal isolation and long-term integrity are ensured.
Sulfate Resisting Cement
Sulfate attack is a major cause of concrete durability issues near coastal areas, industrial wastelands etc. where soils/groundwater contain high sulfate concentrations. Ordinary Portland cement based concrete deteriorates under such sulfate attacking environments. Sulfate resisting cement contains lower C3A content and has less permeability. It also forms less expansive ettringite on reaction with sulfates, thereby maintaining integrity on exposure. It enables durable construction in saline, sulfatic and wastewater contaminated areas.
Low Alkali Cement
Certain types of aggregates like reactive silica can cause expansion and cracking in concrete when used with high alkali cement. This is known as alkali–silica reaction (ASR). Low alkali cement contains controlled amounts of alkalis – sodium and potassium. With a maximum of 0.6% equivalent alkali content, it prevents harmful alkali-aggregate reactions. This ensures long-term durable concrete in structures employing aggregates susceptible to ASR. Surface scaling is also reduced with use of low alkali cement.
High Early Strength Cement
Constructions requiring fast demoulding or early loading necessitate cement providing high early strengths. Pre-stressing of concrete members, repair works and precast construction are such applications. Special additives and optimized mineralogical composition help high early strength cement gain significant strengths within 24 hours, enabling early usage of concrete members. Emergency repair, fast track projects, precast construction benefit from this specialty cement variant.
Low Heat Cement
Massive concrete structures like dams, runways and heavy foundations generate heat of hydration as cement hydrates. If not properly addressed, this can cause cracking of concrete. Low heat cement contains less tricalcium aluminate and optimized mineral chemistry to reduce hydration heat generation by 30-50%. Proper curing is still required but contributed cracking risk is minimized. Thermal stresses are mitigated enabling monolithic pouring of thick concrete sections.
High Sulfate Resisting Cement
Some environments impose very high sulfate concentrations involving secondary sulfate attack after initial sulfate damage. Extraordinary sulfate resistance is required in such cases. Special cements developed with very low C3A, addition of vitrified material like slag and optimized composition provide resistance to concentrations up to 20,000 ppm of sulfates in surrounding environment. They ensure long service life and reliability of structures located close to industrial areas and soil with exceptionally high sulfate bearing salts.
Expansion Cement
Development of cracks in concrete structures can be a major problem for durability. Expansive cement undergoes controlled expansion upon hydration, filling up micro-cracks automatically as they form. The expansion is caused by ettringite or iron oxide formation within cement gel. Cooled expansive concrete remains in compression, denying entry of harmful agents. Cracking is prevented in large concreted areas experiencing stresses or shrinkage effects. Foundations and below-grade structures can be more durable with use of expansion cement.
This variety in specialty cements addresses diversified needs of construction industry and facilitates engineering of durable concrete for diverse applications and exposure conditions. Technological advancements enable tailoring cement characteristics for meeting performance specifications that suit specific project requirements. Specialty cements provide solutions where ordinary cement is inadequate. Their judicious selection and use helps enhance the service life of concrete structures.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
