The Effect of Superabsorbent Polymer and Nano-Silica on the Properties of Blended Cement

Incorporating superabsorbent polymer (SAP), which has the abilities of absorption and desorption in cement mortar, can achieve the effect of internal curing. It is expected that the incorporation of nano-silica will improve the workability and strength in cement mortar/concrete. Hence, this study aims to examine the effect of SAP and nano-silica on the properties of blended cement paste. The experimental investigations via several tests such as consistency, setting time, compressive strength, UPV, and acid test were performed. Based on energy-dispersive X-ray analysis (EDX) test and scanning electron microscopy (SEM) test results, the morphology of hydration products and mineral compositions of cement paste were further analysed, and the mechanism of SAP with 0.2% and 0.3% and NS with lower percentages ranging from 0.5% to 2% on the performance of cement paste was studied. The results exhibited that incorporating SAP in various percentages from 0.5% to 2% prolonged the initial setting time, reduced the fluidity, and increased the water content and formation of pores. In addition, various percentages ranging from 0.5% to 2% of NS were added; thereby, an increase in the hydration process and refining the microstructure was found. The microscopic test results showed that the blended cement paste can effectively improve the denser microstructure and refine the pore structure.

Investigation on the Role of Steel Slag Powder in Blended Cement Based on Quartz Powder as Reference

To clarify the role of steel slag powder in blended cement, steel slag powders with different amounts and particle sizes were mixed into blended cement and the inert quartz powder was selected as the reference. The influences of steel slag powder with different amounts and particle sizes on the hydration and hardening properties of blended cement were studied from hydration heat, nonevaporable water content, porosity, hydration products, and strength. The results show that the influence coefficient of nonevaporable water content (ՓWn) of blended cement paste is in an exponential relationship with the amount of steel slag powder. Moreover, at a dosage of 30%, ՓWn of blended cement gradually decreases with the increase of steel slag particle size. Both the early and late compressive strengths of blended cement are in a binomial relationship with the amount of steel slag powder. The influence coefficient of steel slag powder on the compressive strength of blended cement is negative at the age of 3 days, whereas it is positive at the age of 28 days. The chemical filling effect of 30% steel slag powder with different particle sizes in the blended cement paste is very small, only 1.13%–5.06%. The hydration products of blended cement containing steel slag are mainly amorphous C-S-H gels and platy Ca(OH)2, and their density are consistent with the law of their porosity.