| The rapid development of automobile industry leads to the accumulation of a large number of waste rubber tires,which seriously pollutes the environment.The resource utilization of waste rubber has aroused wide concern in the society.Because rubber has light weight,elasticity,low thermal conductivity and other characteristics,adding the waste rubber powder to the cement-based material can effectively improve the toughness,heat preservation,sound insulation and other properties,and in line with the concepts of energy-saving,environmental protection,green and other for current building materials.However,because the surface of rubber powder is hydrophobic,which is mutually repellent with the hydrophilicity of cement,making it easy to form a large number of pores,can lead to a sharp decrease in the strength of rubber-cement composites.At present,the combination of rubber powder and Portland cement has been widely studied.In view of the disadvantages of magnesium oxychloride cement,such as low toughness,easy warpage and deformation,it is a new research direction to apply waste rubber to magnesium oxychloride cement(MOC)reasonably.In this paper,through the research of modified waste rubber powder,rubber-MOC composite were as the research object,and compatibility of modified rubber powder and MOC was studied,with the strength,density,thermal insulation performance,freezing resistance and the shrinkage performance,which would be conducive to the utilization of waste rubber,and provide theoretical and technical support for the development and application of new cement-based materials The main research results were as follows:(1)Among the five compatibility modification methods,styrene-acrylic emulsion had the best hydrophilic modification effect and the worst method was water-washing modification.Styrene-acrylic emulsion modification was to wrap a layer of hydrophilic film on the surface of rubber powder without changing its structure.Water glass(sodium silicate)modification not only formed a hydrophilic film on the rubber powder film,but also reacted with zinc stearate on the surface,and generated a few cracks.The modification of kh-550 not only grafted hydrophilic groups on the surface of rubber powder,but also performs physical adsorption on its surface.Sodium hydroxide modification was to react with zinc stearate on the surface of rubber powder and corroded the surface,resulting in cracks on the surface.Through hydrophilicity experiment and contact angle test.hydrophilicity of the five methods was obtained(from high to low)as follows: acrylic emulsion >NaOH > kh-550 > sodium hydroxide > water washing.(2)With the increase of the content of rubber powder,the strength of cement increased first and then decreased.At the same time,the fracture pressure ratio was generally on the rise.Compared with unmodified rubber powder,MOC with NaOH modified rubber powder had the best modification effect,and its 28 d flexural and compressive strength increased by 41.2% and 59.6% respectively.The optimum dosage of styrene-acrylic emulsion,kh-550 and sodium silicate was 15%,8% and 20% respectively,and their 28 d flexural and compressive strength increased by 33.7% and 21.3%,40.0% and 17.7%,30.2% and 31.5% successively.When rubber powder was less than 15%,the drying shrinkage of magnesium oxychloride cement could be inhibited.The density and thermal conductivity of MOC mixed with 30% rubber powder decreased by 21.6% and 51.9% respectively.(3)Compared with samples without rubber powder,mixing unmodified rubber powder could improve the porosity of cement structure.Meanwhile,the porosity of cement(from low to high)could be roughly obtained by BET: control sample < NaOH < styrene-acrylic emulsion < water glass < kh-550 < water washing < unmodified rubber powder;Compared with unmodified rubber powder,modified rubber powder could effectively improve the bonding interface with MOC,reduce the porosity of the composites,improve the strength and other performance as well. |
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