Study On Mechanical,Permeability And Self-healing Properties Of ECC Modified With Nano-Silica

The durability of cementitious composites continues to be an issue that receives the attention of practitioners and researchers around the world,which has led to the design of high-performance cementitious composites such as engineered cementitious composites?ECC?.ECCs have high ductility,and they have exhibited considerable self-healing capacities,making them more durable and sustainable for engineering applications.However,for wide and practical applications,further improvement and its cost effectiveness is desirable.This study sought to evaluate the capabilities of ECCs produced with dosages of nano-silica.This was done in relation to the mechanical,transport and microstructural properties of the various specimens that were produced.The materials that were used in the production of the specimens included river sand?maximum grain size 600?m?,Ordinary Portland cement,fly ash,potable water,polyvinyl alcohol fiber,and nano-silica.High range water reducer was also added to improve the workability of the mix.The nano-silica was added to the specimens in 0.0,0.5,1.0,and 1.5 percentages of the combined weight of Ordinary Portland cement and fly ash,which was designated D01,D02,D03,and D04respectively.The objectives and respective results of the study are as follows:1)The compressive and flexural strength properties of the specimens were tested after they had attained 7,14 and 28 curing ages.The approximate average compressive strength of D04 was the highest on the 7^th,14^th,and 28^th with 39,50 and 58MPa respectively.The average flexural strength value of the specimens on the 7^th,14^th,and 28^th days were 13,14,and 16MPa respectively.Ultrasonic Pulse Velocity was also used to evaluate the quality of the various specimens after they had attained 14,21,and 28days of curing.In all the curing ages,the average UPV values of the specimens fell within the marginal range of3.05 to 3.66mm/?s.However,D04 recorded the highest UPV value amongst the specimens and on the 28^th day.2)The water sorptivity test was performed after 28days of curing,where it was observed that the sorptivity coefficients reduced with increased dosages of nano-silica.This observation was different with the sorptivity coefficients of the specimens which had nano-silica dosages,with D02,D03 and D04 recording approximate sorptivity coefficients of preloaded specimens,which were respectively 48%,50%,and 23%higher than their sound specimen counterparts.The sorptivity coefficients were below 0.04mm/min^1/2,which is lower than the values recorded for concrete produced with only Ordinary Portland cement as a binder.3)The effect of nano-silica dosages on the healing capacity of the specimens was assessed with water sorptivity and non-steady state rapid chloride migration coefficient(D_RCM)measurements.Also,Ultrasonic Pulse Velocity?UPV?test was used to assess the effect of healing on the specimens.The specimens were submerged in water for two healing periods,7 and 28 days for the measurement of sorptivity coefficients.There were significant reductions in the sorptivity values of both sound and preloaded specimens after they had been subjected to 7 and 28 days of continuous water.The test results showed improvements in the compressive strength of the specimens with increasing dosages of nano-silica.Nonetheless,the 28th-day flexural strength of the specimens slightly reduced with an increasing amount of nano-silica dosage.It can be concluded from the results of the study that nano-silica can help improve the mechanical and transport properties of cementitious composites.The ability of the material to resist a significant amount of water ingress makes is suitable for civil engineering structures that are exposed to water and other coastal structures.A successful design of ECC with local materials is likely to spur its practical applications in China.