Water-resistance properties of high-belite sulphoaluminate cement-based ultra-light foamed concrete treated with different water repellents

[Display omitted] •We compared the waterproof effect of four types of PWR and two types of LWR on ULFC.•The PWR of CS with 4 wt% dosage reduced the WV and Rf of ULFC most effectively.•The 72 h WV of ULFC using soaked method with HSO and KH550 was reduced to 4.4 wt%. The high water absorption (Wv) of FC, especially ultra-light FC (ULFC), tends to increase the structure burden, reduce the strength, reduce the thermal and sound insulation performance, and make the frost resistance deterioration, which limits its wide development in prefabrication insulation panel industry. In order to effectively reduce the WV at varied water soaking time of ULFC, four types of powdery water repellents (PWR) including calcium stearate (CS), zinc stearate (ZS), polysiloxane (PS) and re-dispersible latex powder (RDL) were doped into high-belite sulphoaluminate cement-based ULFC with dosages varying from 0.5 wt% to 4.0 wt% to prepare water-resistant ULFC with the dry density (ρd) from 270 kg/m3 to 300 kg/m3. Two types of liquid water repellents (LWR) of methyl polysiloxane resin (MPR) and hydrogenated silicone oil (HSO) were used to treat the pristine ULFC by the soaking or surface coating method to explore the water-resistant effect of sole LWR or the combination of LWR and CS on the ULFC. A silane coupling agent (KH550) was further used to promote the LWR to solidify the formation of water-resistant film. The connected pores of ULFC doped with CS, ZS, PS and RDL are effectively reduced; and the pore walls of ULFC doped with CS, ZS and PS become more compact than the control ones. CS, ZS and PS dosage all can reduce the WV of ULFC, and the ULFC doped with 4 wt% CS has the lowest WV of 23.6 wt%, and the strength loss coefficient after saturation is close to 0. The water-resistant effect of LWR is superior to that of PWR, the soaking method is better than surface coating method in reducing WV, and the ULFC treated with HSO and KH550 has the lowest 72 h WV of 4.4 wt% owing to its capillary clogging mechanism, and the corresponding contact angle can reach 125.87°.