Superabsorbent Polymers as an Additive Introducing Hydrophobic Agents into Cement Matrix

Abstract

Addition of hydrophobic agent to cement-based materials while mixing became a frequently used method to improve the stability of final material. Water-repellent is supposed to decrease water absorption and prolong the service life of the material. Such additives are usually added to water, which can affect cement hydration process. The negative influence of hydrophobic agents is frequently observed in decreased compressive strength of hardened concrete. However, a delayed dosage of hydrophobic agent could potentially reduce this negative effect. The presented research aims at verification of this hypothesis. To achieve that superabsorbent polymers (SAP) are used. The analysis was conducted on cement mortar composed of Portland cement with addition of SAP saturated with water containing hydrophobic admixture prior to mixing. One expected that during initial step of hydration SAP would slowly release modified water increasing hydrophobicity of cement matrix without significant reduction of its mechanical strength. To that end four cement mortars were prepared with one dosage of SAP additive (0.2% of cement mass) and one dosage (1%) of commercially available hydrophobic agent based on triethoxyoctylsilane. After 28 days of maturing the compressive strength, Young’s modulus and capillary absorption tests were performed. According to the results, the proposed combination is a promising solution. The compressive strength of samples containing SAP and hydrophobic admixture is approx. 18% higher comparing to mortar without superabsorbent polymer. Simoultanously, results of capillary absorption coefficient indicate that the internal hydrophobicity is maintained. Summing up, the presented research evinces that SAP may be a promising way of introduction other admixtures into cement matrix.