The chemical action of Al(OH)_3 accelerators in the early hydration of Portland cements

摘要

The early hydration of Portland cement with an alkali-free setting accelerator was investigated using DCA, ESEM-EDX, XRD/Rietveld refinement and ICP-OES. The early hydration of the system consisting of cement and Al(OH)_3 accelerator up to 24 hours was modelled. The rapid setting of the cement was caused by intensified formation of ettringite. Because of the rising Al_2O_3/SO_3 ratio the ettringite crystals occur in the form of fibres in the acceleration period. The sulfate agent, the free lime and the clinker provide the calcium for the reactions of the accelerator to form ettringite in the cement-accelerator system. Neither syngenite nor gypsum was formed in the cement-Al(OH)_3 accelerator system in the first 24 hours.