Effect of graphene surface properties on mechanical properties and microstructure of cement mortar composites
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摘要: 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。Abstract: 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.
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Key words:
- graphene oxide /
- reduced graphene oxide /
- mechanical properties /
- hydration products /
- microstructure
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图 3 GO和不同还原条件下rGO的Zeta(ζ)电位绝对值:(a) 固定还原时间(30 min)、不同L-AA浓度(10wt%~70wt%);(b) 固定L-AA浓度(50wt%)、不同还原时间(15~60 min)
Figure 3. Absolute values of Zeta (ζ)-potential for GO and rGO with different reduction conditions: (a) Fixed reduction time (30 min), different L-AA concentrations (10wt%-70wt%); (b) Fixed L-AA concentration (50wt%), different reduction time (15-60 min)
In rGO/x-y, x—L-AA concentration; y—Reduction time
图 4 不同还原条件对rGO/水泥砂浆抗折强度的影响:(a) 固定还原时间30 min、不同L-AA浓度(10wt%~70wt%);(b)固定L-AA浓度为50wt%、不同还原时间(15~60 min)
Figure 4. Effect of different reduction conditions on flexural strength of rGO/cement mortar: (a) Fixed 30 min reduction time, different concentrations of L-AA (10wt%-70wt%); (b) Fixed L-AA concentration of 50wt%, different reduction time (15-60 min)
图 5 不同还原条件对 rGO/水泥砂浆抗压强度的影响:(a) 固定还原时间30 min, 不同L-AA浓度(10wt%~70wt%);(b) 固定L-AA浓度为50wt%,不同还原时间(15~60 min)
Figure 5. Effect of different reduction conditions on compressive strength of rGO/cement mortar: (a) Fixed 30 min reduction time, different concentrations of L-AA (10wt%-70wt%); (b) Fixed L-AA concentration of 50wt%, different reduction time (15-60 min)
图 6 不同还原条件对rGO/水泥砂浆吸水量的影响:(a) 固定还原时间30 min、不同L-AA浓度(10wt%~70wt%);(b) 固定L-AA浓度为50wt%、不同还原时间(15~60 min)
Figure 6. Effect of different reduction conditions on water absorption of rGO/cement mortar: (a) Fixed 30 min reduction time, different concentrations of L-AA (10wt%-70wt%); (b) Fixed L-AA concentration of 50wt%, different reduction time (15-60 min)
图 8 添加GO和rGO的水泥砂浆在28天时的XRD图谱:(a) 固定还原时间30 min,不同L-AA浓度(10wt%~70wt%);(b) 固定L-AA浓度为50wt%,不同还原时间(15~60 min)
Figure 8. XRD patterns of cement mortars with GO and rGO added at 28 days: (a) Fixed 30 min reduction time, different concentrations of L-AA (10wt%-70wt%); (b) Fixed L-AA concentration of 50wt%, different reduction time (15-60 min)
C-S-H—Calcium silicate hydrate
表 1 PO 42.5水泥化学组成
Table 1. Chemical composition of PO 42.5 cement
wt% CaO SiO2 Al2O3 Fe2O3 SO3 MgO Na2O 61.14 22.64 5.18 2.14 2.04 2.22 0.67 表 2 PO 42.5水泥物理性能
Table 2. Physical performance of PO 42.5 cement
Ignition loss/% Initial setting time/min Final setting time/h Specific surface area/
(m2·kg−1)Flexural strength/MPa Compressive strength/MPa 3 days 28 days 3 days 28 days ≤ 5 180 6 351 6.0 8.4 30.4 53.6 表 3 氧化石墨烯(GO)中L-抗坏血酸(L-AA)用量
Table 3. Amount of L-ascorbic acid (L-AA) used in graphene oxide (GO)
No. Mass fraction of
GO/wt%L-AA
concentration/(mg·mL−1)Reaction time/min 1 10 0.11 30 2 20 0.21 30 3 30 0.325 30 4 50 0.54 30 5 70 0.75 30 6 50 0.54 15 7 50 0.54 30 8 50 0.54 45 9 50 0.54 60 表 4 水泥砂浆配合比
Table 4. Mix proportion of cement mortar composites
Sample Cement/g Water/g Sand/g GO or rGO/g NS/g R 100 48 200 0 0.2 GO/CM 100 48 200 0.05 0.2 rGO/0.1CM-30 100 48 200 0.05 0.2 rGO/0.2CM-30 100 48 200 0.05 0.2 rGO/0.3CM-30 100 48 200 0.05 0.2 rGO/0.5CM-30 100 48 200 0.05 0.2 rGO/0.7CM-30 100 48 200 0.05 0.2 rGO/0.5CM-15 100 48 200 0.05 0.2 rGO/0.5CM-30 100 48 200 0.05 0.2 rGO/0.5CM-45 100 48 200 0.05 0.2 rGO/0.5CM-60 100 48 200 0.05 0.2 Notes: rGO—Reduce graphene oxide; NS—Naphthalene superplasticizer; CM—Cement mortar; R—Blank sample group; GO/CM—Add 0.05wt%GO cement mortar sample group; rGO/0.1CM-30—Add 0.05wt%rGO (by 10wt% L-ascorbic acid reduction 30 min) cement mortar sample group; rGO/0.5CM-15—Add 0.05wt%rGO (by 50wt% L-ascorbic acid reduction 15 min) cement mortar sample group. 表 5 rGO水泥砂浆试样rGO/0.5CM-30的水化产物元素组成
Table 5. Elemental composition of hydration products of rGO cement mortar sample rGO/0.5CM-30
wt% Crystal shape C O Ca Mg Al Si S K Fe Needle-like product 1.12 41.14 35.48 1.57 2.62 9.33 3.20 2.66 2.87 Lamella product 3.60 44.19 34.86 0.90 1.61 8.92 2.56 2.16 1.20 Amorphous product 3.24 43.39 35.77 1.06 1.60 8.87 2.90 1.52 1.65 Rodlike product 3.01 46.02 35.61 1.27 1.29 8.12 2.39 1.46 0.82 -
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