Strength and pore characteristics of OPC-slag cement paste mixed with polyaluminum chloride

摘要

An experimental study of ordinary Portland cement mixed with ground granulated blast-furnace slag (OPC-slag) showed varying rates of slag (60%, 40%, and 20% replacement rate to OPC) and polyaluminum chloride (PAC) (0%, 2%, 4%, 6%, 8%, and 10% added to the mixing water) were mixed into the cement to assess the strength and pore structure properties of the cement. X-ray diffractometer, mercury introsion porosimetry, scanning electron microscopy and thermal analysis were performed to observe the pore structures and hydration reactants. As the amount of PAC increased, the compressive strength increased, the total porosity decreased, and the pore volume less than 50 nm diameter increased. PAC promotes hydration of slag particles. The aluminum contained in the PAC also changes the C-S-H gel to a more dense C-A-S-H gel and contributes to the formation of Friedel's salt. And the chloride ion in the PAC forms a Friedel's salt to fill the pores. In this process, portlandite was consumed. 10% PAC showed the highest compressive strength at all slag replacement rates. 20% slag showed 134.6% at 28 days, 151.9% at 7 days for 40% slag, and 159.0% at 1 day for 60% slag. 10% PAC decreased total porosity and increased pores smaller than 50 nm compared to without-PAC sample. In particular, the OPC-slag sample with 20% slag substitution showed the largest pore structure change due to the large and clear reduction effect of pore diameter and volume by PAC. It was confirmed that mixing of PAC with OPC-slag cement paste formed a dense matrix and affected the improvement of compressive strength and the change of pore structure. (C) 2019 Elsevier Ltd. All rights reserved.