PROPERTIES OF PORTLAND CEMENT BASED MATERIALS MODIFIED BY SILICA FUME AND MIXED WITH SATURATED LIME-WATER

On the road of minimizing air pollution and global warming by reducing the Portland cement content in Portland cement based mixes, this experimental study was conducted. Maximizing the percentage of Portland cement replaced by silica fume was tried using lime-water instead of water in mixing. That will help availability of CH crystals at early ages for pozzolanic reaction instead of waiting up to C₃S and C₂S hydration products.
The conducted Portland cement based materials included three groups; cement pastes, cement mortars and cement concrete mixes. The main parameters were; type of mixing solution (water or lime-water) as well as the percentages of Portland cement replaced by silica fume. Times of initial and final settings, compressive strength development, existence and intensity of CH crystals with age, pozzolanic activity as well as efficiency of the investigated matrices to delay the corrosion of embedded steel bars were the investigated properties.
Test results show that using lime-water in mixing delays both of initial and final setting times compared with traditional water due to the common ion effect principals. Moreover, combination use of lime-water and silica fume enhances the pozzolanic reaction that was reflected by the strength development at both early and later ages. The existence of CH crystals for higher percentages of silica fume (up to 30%) for further reaction at later ages was observed by XRD results. Moreover, combined use of silica fume and lime-water ensures a high alkaline media around steel bars from the moment of ingredients mixing as long as later ages despite of pozzolanic reaction that was identified from results of chloride attack.