早强保坍型聚羧酸减水剂的制备与性能研究

基于分子结构设计原理,以甲基烯丙基聚氧乙烯醚(TPEG)、N-羟甲基丙烯酰胺(N-MA)为原料,加入自制含有较多羧基、羟基的功能大分子单体,采用自由基聚合方法,合成了兼有早强和保坍作用的新型聚羧酸减水剂.结果表明:最佳合成工艺条件为n(TPEG)∶n(AA)∶n(N-AM)∶n(大单体)为1∶7∶4∶3,反应温度为60℃,反应时间为4～5h,合成减水剂减水率达32％,混凝土初始坍落度220 mm;2 h坍落度160 mm;1d抗压强度比为185％;3 d抗压强度比为177％.利用红外光谱和凝胶渗透色谱表征减水剂分子结构和分子量,合成分子中含有大量羧基、酰胺基、酯基和醚基,重均分子量均在3.6万左右,数均分子量均在2万左右,分子量分布均匀.采用X射线衍射分析1d龄期水泥试样的水化产物组成,相比于空白试样,掺加减水剂能延缓硅酸盐熟料矿物的水化进程,但促进了AFt的形成,发生AFt向AFm的转变,加快水化速率,具有一定的早强作用.

Synthesis and Properties of Polycarboxylate Superplasticizer with Early Strength and Slump Loss Resistance

According to the principle of molecular design,A new type of polycarboxylate (PC) superplasticizer with early strength and slump loss resistance was prepared by free-radical copolymerization,which selects Prenyl polyxyethylene ether (TPEG),N-Methylol acrylamide (N-MA) as co-monomers and mixed the fuctional macromolecules which contained functional groups of carboxyl (-COOH),hydroxyl (-OH).The result shows that the optimal PC superplasticizer can be obtained at n (TPEG) ∶ n (acrylic acid AA) ∶ n (N-AM) ∶ n (macromolecules) =1 ∶ 7∶ 4∶ 3,the reaction temperature is 60 ℃,the reaction time is 4-5 h,then water reducing rate is up to 32％,the initial slump of concrete can reach 220 mm,the 2 h slump remaines at 160 mm,1 day's ratio of compressive strength is 185％,and 3 day's is 177％.The molecular structure of PC superplasticizer is characterized by Fourier transform infrared spectroscopy and the molecular mass and distribution analysis is characterized by Gel permeation chromatography respectively.The FT-IR shows that the expected functional groups contain a large number of carboxyl,amide,ester and ether bonds in the PC superplasticizer,and the GPC displays that molecular weight distribution of PC are evenly,the weight-average molecular weight (Mw) is about 36000 and the number-average molecular weight (Mn) is about 20000.X-ray diffraction is used to characterize the hydration products of cement.Comparing the adding PC superplasticizer to cement and blank sample,PC superplasticizer can delay the process of hydration of silicate clinker minerals,but can promote the growth of ettringite,the transformation from AFt to AFm,which can improve hydration rate and the early strength.