Cement, Energy & Environment

achieve cement and concrete with tailor made Effect of nano-particles addition on Cement performance Performance • Use of nano-particles for reinforcement of cementitious matrix for improved flexibility and toughness • Application of photocatalytic Ti0 2 nano– particles for self cleaning concrete surfaces • Cement based nano-composites for vari ous applications Salient characteristics of Nano-cements Nano-cements consist of well dispersed nano sized particles of cement and mineral admixtures. The nano particles are evenly distributed among the larger particles of mineral admixtures and with such fine dispersion even a lower content of cement could provide desired binding of aggregates and admixture particles generating required strength and performance. Nano sized particles of cement on account of their large surface area would also hydrate at a much faster rate accelerating strength development. 200 180 :I: f- 160 (.,;) z 140 tool cz:: 120 f- </) \.J 100 2: 80 f- 60 ~ \.J 40 cz:: 20 0 ID 30 70 AGF: (I:"' OAYS) IS:!OPC ~ OPC SS l:'.aO PCMSS 280 Investigations on nano particle blended cements blended with OPC and PPC in different dosages, replacing equal quantity of OPC and their impact on hydration behaviour and performance indicated that dry blending of 3 and 5 % nanosilica resulted in large increase in Blaine's surface area, higher normal consistency and shorter setti ng times of cement blends. Superplasticizer dose of 0.45 to 0.7 % was required for cement blends containing 3 and 5 % nanosilica, for same consistency and w/c ratio as that of control OPC and PPC. The compressive strength of OPC and PPC blends containing 3-5 percent nanosilica was increased by 10 to 49 and 5 to 24 percent respectively, at ages of 1-28 days, over the strength of control OPC I PPC. The relative compressive strengths of OPC and PPC blends containing 5 percent nanosilica/ microsilica are given in Figure 2. Nanosilica was more efficient in causing strength enhancement compared to microsilica . Cement hydration studies using differential thermal analysis (DTA) have indicated pozzolanic reaction of nanosilica at an early age of 1 day. 200 ISO :r 1()0 I f- (.,;) 140 I z ~ 120 1- 100 rn w 80 > f= 60 .-,: ..J 40 ~ 20 0 10 30 70 AGE (DAYS) [IJ>PC 19 PPCNSS s .PPCMSS 280 Fig 1: Relative compressive strength of OPC and PPC blends containing 5 % nanosilica (OPCNS5 and PPCNS5) and 5 % microsilica (OPCMS5 and PPCMS5) The above results indicated possibility of achievi ng significant improvement in the strength characteristics of cementitious binders through blending with nanosized particles of pozzolanic materials. However, handling of nanoparticles and checking any associated health hazards need further consideration. Improvement in performance and durability of concrete through incorporation of nano– particles Substantial improvements in the properties of concrete have been achieved in past by use of silica fume along wi th use of superplasticizers in concrete mixes, leading to very high and ultra high strength concretes . Incorporation of nano-particles in concrete is indicated to result in further improvements in strength and durability characteristics. The average particle size of silica fume is 0.1-0.2 microns which is 100 times finer than the particle size of Portland cement. Nano– particles are still finer having particle sizes of less than 0.1 micron and down to 0.01 microns. The expected influences of nanoparticles on the behaviour of cementitious system have been outlined and include the following : a) Well dispersed nano-particles act as centers of crystallization of cement hydrates, thereby accelerating the hydration b) Nano-particles favour the formation of small sized crystals (such as Ca(OH)2 and Afm) and 6 I