6 – Black liquor waste as a cement admixture or cement and concrete admixtures

Pulp black liquor (PBL) waste, a by-product from paper manufacture, is applied as a cement admixture in two types of cement, namely Ordinary Portland cement (OPC) and Portland limestone cement (LPC). The results show that the consistency of cement pastes premixed with PBL gradually increased with the concentration of PBL, whereas the setting times (initial and final) decreased. Therefore, PBL can be used as an accelerator. The compressive strength increased slightly during the early stages of hydration but sharply during the later stages, particularly when premixed with PBL. The combined water content and bulk density displayed the same trend as the compressive strength, whereas 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. SEM images proved that the incorporation of PBL with cement did not affect the chemical composition of OPC or LPC hydrates, but only the physical state, shape, size, morphology and crystallinity of the formed hydrates. Two weight percent of PBL is the optimum concentration.