Abstract
Chemical functionalization of graphene oxide (GO) is one kind of advanced strategy to eliminate the negative effects on the flowability of cement with GO. The adsorption behavior of admixture on cement plays a vital role in the flowability of cement-based materials. Herein, the comparison study on the adsorption behavior (including adsorption amount, adsorption kinetics, adsorption isotherms and adsorption layer thickness) of three kinds of chemically functionalized graphene oxides (CFGOs) with different polyether amine branched-chain lengths and GO on cement is reported. The results of CFGOs and GO adsorption data on cement particles were all best fitted with the pseudo-second-order kinetic model, and also conformed to the Freundlich isothermal model, indicating that the adsorption of CFGOs and GO on cement both were multilayer type and took place in a heterogeneous manner. The adsorption of CFGOs and GO on cement was not just physical adsorption, but also engaged chemical adsorption. In contrast to GO, the adsorption behavior of CFGOs on cement represented a lesser adsorption amount, weaker adsorption capacity and thinner adsorption layer thickness. Moreover, the longer the branched-chain length of CFGOs, the greater the decreasing degrees of adsorption amount, adsorption capacity and adsorption layer thickness. Due to the consumption of the carboxyl group (-COOH) by chemical functionalization, the anchoring effect of CFGOs was weaker than GO, and the steric hindrance effect generated from branched-chains which weakened the van der Waals forces among CFGOs layers. Moreover, the steric hindrance effect strengthened with the increasing branched-chain length, thus preventing the cement particles from aggregation, which resulted in satisfactory flowability of CFGOs with incorporation of cement rather than GO.
Highlights
In recent years, carbon materials have been widely utilized to improve various properties of cement-based materials [1,2,3,4,5]
The steric hindrance effect strengthened with the increasing branched-chain length, preventing the cement particles from aggregation, which resulted in satisfactory flowability of chemically functionalized graphene oxides (CFGOs) with incorporation of cement rather than graphene oxide (GO)
These results indicate that the GO and CFGO adsorption process cannot be well fitted with the pseudo-first-order kinetic model, but agree with the pseudo-second-order kinetic model
Summary
Carbon materials have been widely utilized to improve various properties of cement-based materials [1,2,3,4,5]. Huang et al [22] reported that GO can considerably improve the compressive strength, flexural strength, and elasticity modulus of concrete, but GO can increase the shrinkage strain of concrete. Most of these works were focused on the optimization of the dosage-dependence of GO on the microstructure and macro-performance on hardened cement-based materials without considering that GO has an adverse impact on the flowability of fresh cement [23,24,25,26]. There is no doubt that good flowability is the precondition of concrete agitation and pump transport, which is a key performance for cement-based materials in engineering applications
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