In the present study, three modification methods, including water washing, sodium hydroxide (NaOH), and styrene–acrylic emulsion, were used to modify waste rubber powders. The influence of rubber powders on the mechanical properties and frost resistance of magnesium oxychloride cement was examined, and the different modification mechanisms were also analyzed. Based on the analysis of hydrophilic properties after modification, styrene–acrylic emulsion achieved the best modification effect, while water washing produced the least modification effect; regarding mechanical properties, magnesium oxychloride cement mixed with NaOH modified rubber powders achieved the best modification effect, in which the 28 d flexural strength and compressive strength increased by 41.2% and 59.6%, respectively. During the freeze-thaw cycles, the mass loss of specimens was reduced with an increase in the content of rubber powders. In addition, after 300 cycles, the relative dynamic modulus of elasticity of the blank sample was about 28.12%, while that of the magnesium oxychloride cement mixed with NaOH modified rubber powders was approximately 42.38%. In general, the properties of the modified rubber powder–magnesium oxychloride cement composite material can meet the requirements for engineering materials, which provides a theoretical basis and technical support for the application of rubberized magnesium oxychloride cement.
This paper presents a new modification of the nanostructure of CaSO4·2H2O crystals containing nanopores. This nanoporous structure was achieved in phosphogypsum samples that were modified by sodium carbonate and alum. The effects of sodium carbonate and alum on the properties of phosphogypsum were studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods were used to explore the micro-mechanism of the composite system. Subsequently, molecular dynamics simulations were used to study the nanopore structures of the modified CaSO4·2H2O. The results show that the addition of sodium carbonate and alum reduced the absolute dry density by 23.1% compared with the original phosphogypsum sample, with a bending strength of 2.1 MPa and compressive strength of 7.5 MPa. In addition, new hydration products, sodium sulfate and sodium aluminum sulfate, were formed in the sample doped with sodium carbonate and alum. A new nanostructure of CaSO4·2H2O crystal containing nanopores was formed. Molecular simulations show that the hydration products were responsible for the surface nanopore formation, which was the main factor leading to an increase in mechanical strength. The presented nanopore structure yields lightweight and high strength properties in the modified phosphogypsum.
Magnesium oxychloride cement foam concrete specimenswere prepared by applying the inorganic-organic composite modification method to improve the water resistance of magnesium oxychloride cement and using the composite protein foaming agent for the purpose of foaming. Then, freeze-thaw cycle test was performed to examinethe frost resistance property of the specimens under the designed mix proportion. The experimental results show that: after 20 freeze-thaw cycles, neither macro-cracks nor hollow spalling are observed on the surface of the specimen, the strength loss rate is only 12%, and the compressive strength remains at a relatively high level of 1.46 MPa. Meanwhile, the microstructure of the specimen before and after the freeze-thaw experiment was analyzed through SEM test, and the failure mechanism during the freeze-thaw process was explained.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.