Effects of Superplasticizers on Flow and Strength of Mortars Using Low-Carbon High Early Strength and Type III Cements

Abstract

This research aimed to investigate the effects of polycarboxylate ether (PCE)-based and sulfonated naphthalene formaldehyde (SNF)-based superplasticizers on the flow spread and compressive strength of mortar mixtures incorporating one brand of low-carbon high-early-strength cement and two brands of Type III Portland cement. Two brands of each type of superplasticizer were used at dosage ranges of 0–1.6% and 0–2.1% by weight of cement for PCE and SNF, respectively. Mortar mixtures were prepared in accordance with ASTM C109 using a water-to-cement ratio of 0.485, a cement-to-sand ratio of 1:2.75, and sand with a fineness modulus of 2.80. Compressive strength specimens consisted of 5×5×5 cm mortar cubes tested at the ages of 18 hours, 3 days, and 7 days.The experimental results showed that mortar mixtures containing PCE-based superplasticizers began to exhibit segregation at approximately 0.8%, with clear segregation observed at approximately 1.2%. In contrast, mortar mixtures containing SNF-based superplasticizers began to exhibit segregation at approximately 1.4%, with more pronounced segregation occurring at approximately 1.7%. Consequently, the flow spread increased until reaching its maximum value before decreasing when the superplasticizer dosage exceeded the optimum adsorption level, resulting in instability within the mortar system. At high superplasticizer dosages, the compressive strength tended to fluctuate and become unstable due to segregation and bleeding, which caused a non-uniform internal structure and increased porosity within the mortar. However, within the appropriate dosage range, the compressive strength tended to increase due to improved cement particle dispersion and the development of a denser internal structure.Furthermore, mortars containing low-carbon high-early-strength cement combined with PCE-based superplasticizers exhibited relatively high and consistent flow spread values. In addition, mortars containing low-carbon high-early-strength cement showed higher flow spread values than those containing Type III Portland cement when the same dosage of SNF-based superplasticizer was used.