Whether so-called Mg[sbnd]Si gels are produced under dolomite-quartz system under alkaline conditions

Micro-crystalline to crypto-crystalline quartz exists always in dolomitic limestones. When the dolomitic limestones are used as aggregates of concrete, pore solutions mainly composed of K⁺, Na⁺, Ca²⁺ and OH⁻ ions may interacts simultaneously with dolomite and micro-crystalline to crypto-crystalline quartz. To understand mechanisms of alkali-silica-dolomite reactions in concrete, chemical reaction products in system of CaMg (CO₃)₂-SiO₂-Ca(OH)₂-KOH-NaOH-H₂O cured at 20 °C, 38 °C and 60 °C were analyzed by X-ray diffraction, infrared spectroscopy, differential scanning calorimeter-thermo gravity and scanning electron microscope. Results show that magnesium derived from dolomite was mainly incorporated in brucite and silicon derived from micro-crystalline to crypto-crystalline quartz was in alkali-silica gel. No evident magnesium silicate gels were detected under high alkaline condition. It is expected that magnesium silicate gels will not be formed accompanying with alkali-silica/dolomite reaction in concrete. Reaction in dolomite-quartz system is a superposition of ASR and ACR.