Synthesis of polycarboxylic ether superplasticizers based on the high conversion of EPEG in a transition metal oxide heterogeneous catalytic system
The existed polycarboxylic ether superplasticizer (PCEs) that mainly synthesized in a homogeneous catalytic synthesis has the disadvantages of low conversion rate and poor performance stability. In this paper, high performance PCE-1–5 were synthesized via a heterogeneous H 2 O 2 -ASA (ascorbic acid) redox system catalyzed with MnO 2 , Fe 2 O 3 , Co 2 O 3 , Ni 2 O 3 and ZnO respectively. GPC data show that the molecular weights of PCE-1–5 are higher than that of PCE0 (synthesized via a H 2 O 2 -ASA redox system without transition metal oxides). HPLC indicates that the conversion rates of macromonomer for PCE-1–5 are up to 99.81%, which is 27.47% higher than that of PCE0 (72.34%). As results, PCE-1–5 have a good dispersibility, high water reducing rate and are much benefits to the early hydration of cement paste and the strength of concrete. The mechanism research shows that the cement samples doped with PCE-1–5 have a larger zeta potential , stronger complexing ability with Ca 2+ , and thicker adsorption layer that is as high as 1.03 nm, which makes the spread diameter of cement paste as high as 309 mm. In addition, the obtained microstructure is much denser as is reflected by the nanometer pore size of hardened cement paste (12.26 nm), which makes the 28 d compressive strength of cement test block as high as 60.19 MPa. Generally, the heterogeneous transition metal oxide catalytic redox system provides a good choice for the synthesis of PCEs.
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