Utilization of Pulp black liquor waste as a cement admixture
The pulp black liquor waste (PBL), a byproduct from paper-making, is applied as a cement admixture in two types of cement, namely Ordinary Portland cement (OPC) and Portland limestone cement (LPC). The results showed that the water of consistency of cement pastes premixed with PBL was gradually increased with the concentration of PBL while the setting times (initial and final) were decreased. So, it can be used as an accelerator. The compressive strength increased slightly during the early ages of hydration but sharply during the later ages, particularly with those premixed with PBL. The combined water content and bulk density displayed the same trend as the compressive strength, whilst the apparent porosity decreased at all curing times. The IR spectra of cement pastes showed that the intensities of the different peaks of cement pastes with PBL are higher than those of the pure samples. The SEM images proved that the incorporation of PBL with cement did not affect the chemical composition of OPC or LPC hydrates, but it only affected the physical state, shape, size, morphology and crystallinity of the formed hydrates. The 2 wt. % of PBL is the optimum concentration.