Effect of using nano-silica on the rheological, fresh and strength characteristics of cement-based grout for grouting columns

Abstract

For ground improvement via grouting, the rheological abilities of nano-silica (NS) added to Portland cement (PC) based-grouts have been investigated at a wide range of NS replacements (0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%) and water/binder (w/b) ratios (0.5, 0.75, 1, 1.25, 1.5) by conducting the rheometer tests. Using proper grouts from the rheology, then, the fresh and unconfined compressive strength (UCS) tests were performed to criticize the adequacy of NS replacements. From the rheology, the shear stress, apparent viscosity, yield stress and plastic viscosity of PC grout with NS demonstrated that using low to moderate dosages (<2.5%NS) particularly at the consistency of w/b = 1 yielded more favorable flow required high attention at high shear rates. From the fresh tests (w/b = 1), the favorite NS dosages of rheology (<2.5%NS) were also obtained from the workability of mini-slump, flow time and setting time, while the bleeding tests ensured the stability of grouts (<5%) for moderate to high NS rates. Hence, for both the rheology and fresh effects (w/b = 1), the moderate replacements (1.5%NS-2%NS) appeared better for flow issues. From the strength tests (w/b = 1, 28-day) with increasing NS, UCS of PC grout (1.26 MPa) proportionally increased up to 2%NS as an optimal dosage of peak strength (6.92 MPa), then gradually decreased to 4.82 MPa from the peak. The UCS efficiency of moderate NS rates corroborated their flow abilities. All NS dosages sufficiently provided the limit of bearing strength (>0.4 MPa) in ground enhancement. For the optimal rate (2%NS), increasing the curing times (3-day to 28-day) increased the UCS markedly as evidence of NS on the strength quality, and offered the 7-day for the early age of strength development. The failure patterns and SEM images also promoted the effects of NS. The research from the flow and strength findings not only demonstrated the promising effects of NS for grouting, but also offered some insights into designs and applications of foundation works.