The Impact of Plasticizers on the Nature of the Alkali-Silicate Corrosion in Cement Composites

Abstract

This research work attempts to reveal the mechanism of alkali corrosion in cement composites in the presence of plasticizers based on polycarboxylates (PCE), naphtha-lene-formaldehydes (SPNF), and lignosulfonates by maintaining a high pH of the liquid phase and additionally containing monovalent alkali earth metals in cement stone, as well as stopping this process by introducing an active mineral additive. ASR is studied by changing the relative strain with time according to ASTM C-1260. Deformation changes were confirmed by SEM and RFA studies of hydration products and ASR in the microstructure. Separate use of PCE plasticizers in the cement composition increases deformation by 50% to the 56th day; the use of SPNF increases deformation by 10% compared with the additive-free composition. The use of PLS reduces the relative deformation by 25%. The introduction of silica fume into cementitious composites containing plasticizers actually stops ASR only for a short time. A reduction in deformation during MC use together with plasticizer based on naphthalene sulfonate and polycarboxylate occurs only when the dosage of MS is increased to 20–30%; at a lower dosage, the effect is negative, which also affects the phase composition of the composites. The introduction of MC increases the value of the relative deformation compared with plasticizer compositions based only on PLS. SEM studies have detected microcracks and dense fine-crystalline silicate gel, which cause deformation changes in cement composite samples. Research has shown that concrete modified with SPNF and PCE at the maximum dosage of MC (30%) has minimal deformation rates and can be used to select optimal concrete compositions. The results of this study could help to minimize risks, prevent unacceptable expansion, and ensure the high quality of concrete and concrete products during their use as part of various nature-modifying additives.

Keywords

• alkali-silicate reaction (ASR)
• relative deformation
• superplasticizer
• microsilica
• microstructure