石墨烯表面性质对水泥砂浆复合材料力学性能和微观结构的影响

近年来，利用石墨烯及其衍生物改善水泥基复合材料性能受到了广泛关注。但是，关于石墨烯表面性质对水泥基材料的性能影响却鲜有报道。为此，采用不同浓度的L-抗坏血酸(10wt%、20wt%、30wt%、50wt%和70wt%)和还原时间(15 min、30 min、45 min和60 min)将氧化石墨烯(GO)转化为还原氧化石墨烯(rGO)，然后以相同剂量(水泥质量的0.05%)加入到水泥砂浆复合材料中，研究了不同还原程度的rGO对水泥砂浆力学性能的影响。测试结果表明，通过50wt%L-抗坏血酸还原30 min制备的rGO的加入使水泥砂浆28天抗压强度和抗折强度相比于普通试样分别提高了36.84%和43.24%。SEM等分析表明，GO和不同还原程度的rGO均可促进Ca(OH)₂的结晶和水化硅酸钙凝胶(C-S-H)中二氧化硅四面体的形成，形成致密的微观结构。但存在一个最佳阈值(即通过50wt%的L-抗坏血酸还原30 min)，在该阈值下，有利于rGO表面官能团与水化产物的结合。 

Effect of graphene surface properties on mechanical properties and microstructure of cement mortar composites

In recent years, the use of graphene and its derivatives to improve the properties of cementitious composites have received much attention. However, there are few reports on the effect of graphene surface properties on the performance of cement-based materials. Graphene oxide (GO) was converted to reduced graphene oxide (rGO) using different concentrations of L-ascorbic acid (10wt%, 20wt%, 30wt%, 50wt% and 70wt%) and reduction time (15 min, 30 min, 45 min and 60 min) which was then added to the cement mortar composites at the same dosing level 0.05% (by weight cement). The effects of different degrees of reduced rGO on the mechanical properties of cement mortar were investigated. The test results show that the incorporation of rGO prepared by 50wt% L-ascorbic acid reduction 30 min increases the 28 days compressive strength and flexural strength of cement mortar by 36.84% and 43.24%, respectively, compared to the normal specimens. SEM and other analyses show that both GO and rGO with different degrees of reduction could promote the crystallization of Ca(OH)₂ and the formation of silica tetrahedra in hydrated calcium silicate gels (C-S-H) to form dense microstructures. However, an optimal threshold exists (i.e., 30 min reduction by 50wt% L-ascorbic acid). At this threshold, the binding of rGO surface functional groups to hydration products is favored.