Improvement in hygroscopic property of macro-defect free cement modified with hypromellose/potassium methyl siliconate copolymer and pulverized fly ash

Macro-defect-free (MDF) cement composites are high-strength materials produced by applying high shear to cement-polymer pastes, using twin roller mill under moderate pressure and temperature. However, sensitivity toward moisture, specifically degradation of strength on water exposure, is a serious problem associated with MDF cement composites. To address this issue, a novel formulation of Portland cement-based MDF cement composites with addition of potassium methyl siliconate (PMS)–hydroxypropyl methylcellulose (HPMC) copolymer and pulverized fly ash (PFA) is presented. The experimental program involves preparation of first, HPMC/PMS copolymer using magnetic stirrer and then mixing it with cement and PFA to make MDF composites. PMS proportion varies from 0 to 4% in steps of 1%, while 30% PFA was added as cement replacement. Control mix contained 100% cement without PFA and PMS polymer. MDF composite sheets were prepared through twin roller mill and then characterized using FTIR, TGA/DTG and SEM. Flexural strength of MDF composites sheets were estimated by three-point loading test with 1 mm min −1 . loading ramp. Results revealed that PFA/PMS addition have beneficial effects on the flexural strength, temperature and water resistance characteristics of MDF cement composites. FTIR spectroscopy showed the formation of new peaks related to Si–O–Si and Si–CH 3 stretching. PFA/PMS-based MDF composite specimen showed comparatively higher quantity of calcium silicate hydrate gel and lower calcium hydroxide content which resulted in denser microstructure. Inclusion of 30% PFA and 3% PMS in MDF cement matrix produced composites with 52% improved flexural strength and 80.3% water resistant properties as compared to reference MDF mix at 28 days. Graphical abstract