Adsorption Of Polycarboxylate Water Reducer By Porous And Layered Aggregates And Its Effect On Rheological Properties Of Mortar

Aggregate is the second largest consumption of natural resources globally,which takes more than 70%of parts in concrete mix.With the rapid development of infrastructure construction,environmental pollution and river ecological environment damage caused by mining are increasingly prominent,the replacement of natural river sand by manufactured sand has become a trend.Manufactured made sand is made from broken rock.The characteristics of rock and the layered clay impurities in sand will affect the workability of concrete.As an important node of China's "One Belt And One Road" strategy,Africa has witnessed a boom in infrastructure construction projects,which has generated a huge demand for concrete.The quality of local coarse aggregate is unsatisfactory,of which the water absorption rate is about 2%?5%which far exceeds the requirement of national standard(<2%).Large bibulous coarse aggregate and layered clay have a strong impact on the dispersion effect of polycarboxylate superplasticizer(PCE)to the binding materials and lead to a negative effect on concrete workability,even leaving serious hazards on the quality of the project.Adsorption of polycarboxylate water reducer PCE-1 onto porous and layered aggregates and rheological properties of mortar were researched to solve the concrete workability problems caused by porous and layered aggregates.PCE-1 was synthesized via copolymerization using acrylic acid(AA)and acrylic methyl allyl polyoxyethylene ether(HPEG),n(AA):n(HPEG)was 3.2:1.The adaptive problem between PCE and LBSP was analyzed systematically by mortar performance.Main research results and contents of this paper as below:(1)The adsorption isotherm of PCE-1 on the surface of LBSP could be described well by Langmuir model that rising temperature was favorable for adsorption.The adsorption capacity increased first and then decreased with the extension of time and tended to balance at 30min.The adsorption behavior of PCE-1 on the surface of LBSP was proved by pore structure analysis and thermo gravimetric analysis.The PCE/LBSP compound showed a reduction of both pore diameter and pore size due to the presence of PCE in the LBSP pores.(2)The mortar pastes mixed LBSP displayed the typical character of non-Newtonian fluid.LBSP increased slurry viscosity.However,PCE-1 reduced slurry's apparent viscosity.The viscosity of mortar with sinked particles could be improved by AMPS-NNDMA.The viscosity of mortar increased with the prolonging of hydration time.Rheological models displayed that the yield stress was increased by increasing the dosage of LBSP and AMPS-NNDMA copolymer,while decreased by PCE-1.(3)The adsorption isotherm curve was better in line with the Langmuir model,which means raised temperature was favorable for adsorption.The adsorption process of PCE-1 on the surface of the bentonite conformed to the Pseudo-second-order model.The Zeta potential of bentonite decreased with the concentration increased of PCE-1 and poly(vinyl alcohol).X-ray diffraction(XRD)results showed that(001)layer spacing of bentonite changed from 1.24 nm to 1.65 nm after mixed PCE,the(001)layer spacing of bentonite absorbed both PCE-1 and PVA become 1.55 mm.It demonstrated that the intercalation between PCE-1 and bentonite could be prevented by PVA.(4)The mortar containing bentonite was in accordance with the characteristics of non-Newtonian fluid.The viscosity of mortar showed increment by increasing the dosage of bentonite caused by the bridging effect from bentonite particles.It was got opposite results when adding PCE-1 to the slurry mortar due to its dispersibility.Slurry viscosity slightly increased at first then decreased with the concentration of poly(vinyl alcohol)increase.After fitting three kinds of model rheological parameter,the result showed that the yield stress of cement mortar increased as the dosage of bentonite increased and the hydration time extended,while decreased by an incremental dosage of PCE-1 and poly(vinyl alcohol).(5)LBSP and bentonite could reduce the initial fluidity of mortar and reduce the sensitivity of mortar to water and PCE-1.The effect of bentonite on mortar performance was more significant than LBSP.Bentonite only needed 1/6?1/10 dosage of LBSP to get the same effect due to the adsorption amount of bentonite on PCE-1 higher than LBSP.The fluidity loss ratio of mortar with bentonite could be reduced by increasing the dosage of PCE-1 or poly(vinyl alcohol).Fluidity increased and flow rate decreased while yield stress increased.The correlation between flow rate and rheological parameters such as yield stress and viscosity was better than fluidity.AMPS-NNDMA copolymer could inhibit bleeding in mortar with high replacement LBSP,and could effectively reduce the shrinkage of mortar containing bentonite.Polycarboxylate water reducers named PCE-2 and PCE-3 were designed and synthesized,PCE-2 was synthesized via copolymerization using AA and HPEG,n(AA):n(HPEG)was 3.2:1,PCE-3 was synthesized via copolymerization using maleic acid(MA)and isopentenol polyoxyethylene ether(TPEG),n(MA):n(TPEG)was 1:1.Compared with PCE-1,PCE-2 and PCE-3 owned a denser side chain and lower acid to ether ratio.The adsorption capacities of PCE-2 and PCE-3 on LBSP were decreased due to that the hydrodynamic diameters of both polymers were bigger than PCE-1.The adsorption capacity of PCE-3 on bentonite was lower than PCE-1 caused by higher electrostatic repulsion.The dispersion ability of polycarboxylate water reducer with low acid to ether ratio in mortar mixed with adsorptive powder was weakened,and the fluidity retention ability increased.With the combination of polycarboxylate water reducer with different acid to ether ratio,the dosage of polycarboxylate water reducer was decreased,and the fluidity retention ability was improved,which has strong practicability.