The construction industry is undergoing rapid changes with advanced construction techniques and materials. While traditional cement has served well for common constructions, special projects demand special cement varieties with enhanced properties. Speciality cements have thus emerged as one of the key successes in the cement industry, catering to highly specialised construction needs through novel formulations and production technologies. This article explores the various types of speciality cements available today and their specific uses in modern infrastructure and other specialised construction works.

High-Performance Concretes

One of the major categories of Specialty Cement
is high-performance concrete (HPC). Produced using special blend formulations and micro additives, HPC offers higher strength than conventional concrete along with improved workability and durability. With compressive strengths ranging from 40-150 MPa, HPC allows for construction of tall buildings, bridges and other infrastructure requiring high load-bearing capacity in smaller volumes. The enhanced strength is achieved through low water-cement ratio and pozzolanic or latent hydraulic additions that improve microstructure. HPC finds extensive use in high-rise construction, pre-cast elements and other pre-stressed concrete structures.

Another variant is self-consolidating concrete (SCC) which has excellent flow-ability without any vibration or compaction. SCC allows filling of intensely reinforced structures and narrow sections without compromise on strength. It is widely used for pre-cast elements where formwork consolidation is challenging. SCC production requires special cement formulations developed after vigorous rheology tests to achieve the desired self-levelling properties essential for its characteristic self-compaction.

Sulphate-Resisting Cements

In areas with aggressive sulphate soils or where groundwater contains high sulphate, conventional concrete tends to deteriorate rapidly due to sulphate attack. Special sulphate-resisting Portland cements (SRC) have been developed to prevent such deleterious reactions. By controlling C3A levels below 5% and employing pozzolanic or slag additions, SRC obtains better sulphate resistance compared to ordinary Portland cement. It finds application in sewerage works, dams, tanks and other structures in contact with sulphate-laden environments. Careful selection of reactive additives in SRC production enables durability even in highly sulphate-laden conditions.

Low Alkali Cements

Concretes containing high alkali Portland cements can develop reaction with aggregates containing certain types of silica,leading to cracking and expansion over time. Such alkali–silica reaction (ASR) severely hampers durability. Low alkali cements contain alkali content lower than 0.6% Na2Oeq helping prevent harmful ASR. They are used in structures employing aggregates susceptible to alkali reactivity such as certain granites and rhyolites. The stringent control on alkali levels below the threshold limit during manufacture of low alkali cements contributes significantly to achieve desired ASR resistance.

White and Coloured Cements

Though grey in colour, ordinary Portland cement can discolour finished concrete structures and masonry works. Whitening is achieved through selective substitution of clinker by white raw materials like white cement clay or limestone. Finely tuned substitution ratios are required to maintain colour consistency along with requisite strength and hydration properties. Coloured variants are also produced through carefully regulated addition of mineral pigments to obtain different shades like cream, red, blue etc. meeting aesthetic requirements in modern architecture. White and coloured cements have extensive applications ranging from architectural facades to indoor wall claddings.

Other Special Cements

Oilwell cements are designed specifically for cementing casing, liners and drilling pipes inserted in oil and gas wells. Produced through additions of pozzolans or slag, they develop high early strength for quick setting in downhole conditions and also provide zonal isolation between fluid zones. Expansive cements contain hydration swelling materials like ettringite, calcium sulphoaluminate that impart controlled expansion compensation for cracks or minor settlement effects in concrete. Microfine cements are ultra-finely ground with particles below 10μm, enhancing fluidity and strength development apart from reduced porosity. They are utilised in grouts and repair mortars.

With growing specialisation across construction, speciality cements have emerged as a key factor enabling advanced infrastructure projects worldwide. Through optimised formulations encompassing supplementary cementitious materials, mineral admixtures and micro additions – special cements cater to highly specialised performance needs beyond the scope of normal cements. Continuous research is expanding the array of speciality cements to assist novel construction techniques, demanding use environments and rising architectural trends. They are surely propelling cement technology into the future through advanced material science and nanoscale tailoring of microstructures.

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