Effect of organo-mineral additives on physical-mechanical properties and corrosion resistance of sand-cement mortars

Abstract

Introduction. TConstruction of large-scale offshore structures in the coastal area of Vietnam requires new compositions of binders for hydraulic concretes, advanced concrete mixing technologies, and concrete transportation to depositing sites. Materials and methods. The binder, containing sulfate resistant Portland cement and finely dispersed mineral additives, including low calcium fly ash of TPP “Vung Ang” and silica fume SF-90 (SF-90), was added to the mortar mix, and the same about SR 5000F superplasticizer and quartz river sand. Powder particle shape and size were measured using laser granulometry; X-ray diffraction was employed to identify the mineral composition of sulfate-resistant cement; the effect of multi-component organo-mineral additives on the phase composition of the cement stone was studied using methods of thermogravimetric analysis; the absolute volume method was employed to analyze the composition of the mortar. Results. The co-authors have analyzed the application of new compositions of multi-component organic-mineral additives whose content, if taken as a percentage of the cement weight, reaches 1.1–1.45 % of SF 5000F superplasticizer, 10–15 % of SF-90, and 30 % of fly ash. New additives accelerate compressive and tensile strength development by 1.4–1.9 times, and that’s been confirmed by bending early-age and 28-day cement-sand mortar specimens, that have sulfate-resistant cement, and their benchmarking against control specimens. It’s been identified that SF-90 and fly ash, if added to the mix, reduce the Portlandite content in the cement stone by 1.27–3.29 % at the age of 28 days in comparison with the benchmark composition due to their high pozzolanic activity Conclusions. Testing results enable co-authors to recommend the application of multi-component organo-mineral additives to increase the resistance of cement-sand compositions to sulfate corrosion due to the denser structure and lower porosity of the cement stone, caused by the lower value of the water/binder ratio and the packing of pore spaces with active mineral fillers. Therefore, new additives are recommended for use in the production of corrosion resistant concretes suitable for construction of offshore hydraulic structures in Vietnam.