| Polymer-modified waterproof cement mortar(PWCM) has been widely used for waterproofing in public and civil construction and buildings, owing to its good toughness, high bond strength, excellent water resistance, and so on. However, the commercial polymers for PWCM have some disadvantages of high cost, large dosage or poor modification effect. As a resulst of these shortcomings, the PWCM market share is still low. In this paper, the functional core-shell styrene-acrylic copolymer was synthesized by emulsifier-free emulsion polymerization, avoiding the use of emulsifiers. This emulsion was provided with good performance and was environmentally friendly. Using core-shell styrene-acrylic copolymer as the modifier, a new polymer-modified waterproof mortar was developed with steel slag, iron tailings and fly ash as aggregates. The main work and conclusions can be summed up in the following aspects:With styrene(St), hydroxyethyl methacrylate(HEMA) as main materials, a core-shell poly(styrene-hydroxyethyl methacrylate)(PS-HEMA) copolymer was synthesized by emulsifier-free emulsion polymerization. The particle size was about 400~500 nanometers, but the solid content was low, only 4%. The optimal production conditions were determined by reaction time, 5h; NaOH and NaHCO3, 1:1; potassium persulfate(KPS), 1.0%~1.8%; HEMA, 11%~13%(based on the St weight). In addition, a poly(styrene-sodium p-styrenesulfonate-hydroxyethyl methacrylate)(PS-NaSS-HEMA) copolymer with high solid content was synthesized by emulsifier-free emulsion polymerization. The copolymer maintained the original core-shell structure, and the particles size was about 70~80 nanometers. The optimal production conditions were determined by sodium p-styrenesulfonate(NaSS) 0.8%~1.2%(based on the styrene mole) and St: H2 O 1:4~3:10, respectively. The solid content reached 20%, which greatly improved production efficiency and reduced cost.The reasonable gradation of composite aggregate was: iron tailings, 40%; steel slag, 40%; fly ash, 20%. Using cement, composite aggregate, PS-HEMA and some additives as main materials, a new styrene-acrylic polymer-modified waterproof mortar was prepared. The effects of cement-aggregate ratio, polymer-cement ratio, defoamer-cement ratio and water reducing agent-cement ratio on performances of this mortar were investigated. The factor design was used to determine the optimal conditions: polymer-cement ratio, 12 wt.%; cement-aggregate ratio, 1:2.5; defoamer-cement ratio, 0.8wt.%. The product conformed to Chinese norms. In addition, according to the optimal formula, the waterproof mortar was produced by PS-NaSS-HEMA with high solid content as modifier, it also conformed to Chinese norms, and the water resistance was better. Furthermore, the mortar with PS-HEMA as the modifier gave better mechanical properties and water resistance compared to those with commercial ethylene-vinyl acetate copolymer(EVA) and styrene-acrylic copolymer(SAE) as modifiers.The polymer-modified waterproof mortar and the polymer structures were characterized by FTIR, SEM and TEM. FTIR spectrum showed that all the monomers of St/HEMA and St/Na SS/HEMA system participated in reaction and the styrene-acrylic copolymers were produced. SEM photograph indicated that polymer particles with well dispersibility were spherical and homogeneity. TEM photograph proved that polymer microspheres had obvious core-shell structure. The microstructure of mortars was analyzed by SEM. It revealed that the polymer membranes covered the surface of cement hydration products, micro-cracks and holes. The polymer membranes also encapsulated the cement grains and aggregate. Some polymer microspheres obstructed the fine pore network inside of hydrates and filled the large pores. All above effects combined to improve the mortar’s strength, especially water resistance. |
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