使用喷射超高韧性水泥基复合材料(Ultra High Toughness Cementitious Composites,UHTCC)加固和修补水工混凝土结构具有广阔的应用前景。为评估加固效果,采用喷射UHTCC和既有混凝土制备成的两端无切口剪切型断裂复合试件,开展单边加载...使用喷射超高韧性水泥基复合材料(Ultra High Toughness Cementitious Composites,UHTCC)加固和修补水工混凝土结构具有广阔的应用前景。为评估加固效果,采用喷射UHTCC和既有混凝土制备成的两端无切口剪切型断裂复合试件,开展单边加载剪切型断裂试验,测试两种材料的界面剪切型断裂韧度。对既有混凝土表面分别采用高压水枪冲洗、人工凿毛和涂抹界面剂三种不同的处理方法,并对比研究喷射UHTCC和浇筑UHTCC两种施工工艺,探究不同因素对复合试件界面剪切型断裂韧度的影响。试验结果表明:喷射UHTCC与既有混凝土之间黏结性能良好;界面粗糙度对界面剪切型断裂韧度无显著影响;涂抹界面剂会使界面剪切型断裂韧度显著下降;喷射UHTCC制备的复合试件其界面剪切型断裂韧度高于浇筑UHTCC制备的复合试件。喷射UHTCC技术可对水工混凝土结构进行有效的加固和修复。展开更多
Nano particles have been found to be effective in enhancing many properties of regular concretes. However, there is little information on the effect of nano particles on shotcrete. In fact, if similar positive effect ...Nano particles have been found to be effective in enhancing many properties of regular concretes. However, there is little information on the effect of nano particles on shotcrete. In fact, if similar positive effect of nano particles can also appear in shotcrete, they will greatly benefit the wide application of shotcrete in more and more repair and strengthening of structures in civil engineering, especially in corrosive environments. In this study, through experiments on 70 specimens, the effects of nano SiO2, CaCO3 and Al2O3 particles on the early-age porosity, pore size distribution, compressive strength and chloride permeability of shotcrete were investigated.Test results indicated that nano SiO2 particles significantly increased the compressive strength and chloride penetration resistance; nano Al2O3 and CaCO3 particles had slight enhancing effect on the compressive strength; nano CaCO3 particles were most effective in promoting the chloride penetration resistance of shotcrete. As a conclusion, nano SiO2 particles were recommended when both early age compressive strength and chloride penetration resistance were crucial, and nano CaCO3 particles were recommended when only chloride penetration resistance was concerned for their high cost-effectiveness.展开更多
UHTCC (ultrahigh toughness cementitious composite), which is a kind of ultrahigh toughness cemen- titious composites material, exhibits pseudo strain hardening feature when subjected to tension load, and has enormous ...UHTCC (ultrahigh toughness cementitious composite), which is a kind of ultrahigh toughness cemen- titious composites material, exhibits pseudo strain hardening feature when subjected to tension load, and has enormous ductility and prominent crack dispersal ability. Accordingly, UHTCC can improve mechanical behavior of ordinary concrete structure especially its durability, and has been regarded as historical breakthrough to traditional cementitious materials. In this paper, the study focuses on flexure behavior of steel reinforced beam made of UHTCC. Based on the plane section assumption, along with two equilibrium equations of force and moment, the formulae to calculate the flexural load capability for the reinforced ultrahigh toughness cementitious composite (RUHTCC) beam were developed under the assumption that the compression stress- strain relationship in the UHTCC material is a bilinear model. Following this, the simplified formulae were further evolved by effective rectangle stress distribution approach in order to facilitate design of practical engineering. Two effective parameters introduced in effective rectangle approach were determined. The mathematical expressions to evaluate limited rein- forcement ratio, flexural stiffness as well as ductility index were proposed, too. Last, two series of dif- ferent reinforcement ratios of the RUHTCC beams were tested in four-point flexure loading. For com- parison purposes, ordinary RC (reinforced concrete) beams also were prepared. Both moment curva- ture curves and load mid-span displacement curves were recorded and compared with the theoretical calculations. A good agreement between them was found, which validates the proposed theoretical formulae. For ductility index, a slightly big difference between the experimental values and the calcu- lated ones exists. The experimental results show that, compared to control RC beams, the RUHTCC beam can improve both flexural capacity and ductility index, and the degree of improvement will de- crease with the increase in the reinforcement ratio. Particularly, the results also reveal that lager crack width in control beams can be greatly reduced by formation of tightly-spaced fine cracks in UHTCC, which offers more durable structures.展开更多
Based on the concept of functionally graded concrete,UHTCC(ultrahigh toughness cementitious composites)material with excellent crack-controlling ability is strategically substituted for part of the concrete,which surr...Based on the concept of functionally graded concrete,UHTCC(ultrahigh toughness cementitious composites)material with excellent crack-controlling ability is strategically substituted for part of the concrete,which surrounds the main longitudinal reinforcement in a reinforced concrete member.Investigations on bending behavior of such a functionally graded composite beam crack-controlled by UHTCC(abbreviated as UHTCC-FGC beam)have been carried out.After establishing a theoretical cal-culation model,the paper discusses the results of four-point bending experiment on long composite beams without web reinforcement,and validates the theoretical formulae through experimental results of UHTCC-FGC beams with different thicknesses of UHTCC layer.Besides improving bearing capacity and saving steel reinforcements,the results indicate that UHTCC-FGC beams can also effectively control the deformation and enhance the ductility of members.At last,the optimal thickness of UHTCC layer in UHTCC-FGC beams has been confirmed,which can not only save materials and improve mechanical performance of members,but also be very effective in preventing corrosion-induced damage and enhancing the durability of members by controlling crack width below 0.05mm under service conditions.展开更多
文摘使用喷射超高韧性水泥基复合材料(Ultra High Toughness Cementitious Composites,UHTCC)加固和修补水工混凝土结构具有广阔的应用前景。为评估加固效果,采用喷射UHTCC和既有混凝土制备成的两端无切口剪切型断裂复合试件,开展单边加载剪切型断裂试验,测试两种材料的界面剪切型断裂韧度。对既有混凝土表面分别采用高压水枪冲洗、人工凿毛和涂抹界面剂三种不同的处理方法,并对比研究喷射UHTCC和浇筑UHTCC两种施工工艺,探究不同因素对复合试件界面剪切型断裂韧度的影响。试验结果表明:喷射UHTCC与既有混凝土之间黏结性能良好;界面粗糙度对界面剪切型断裂韧度无显著影响;涂抹界面剂会使界面剪切型断裂韧度显著下降;喷射UHTCC制备的复合试件其界面剪切型断裂韧度高于浇筑UHTCC制备的复合试件。喷射UHTCC技术可对水工混凝土结构进行有效的加固和修复。
基金Funded by National Natural Science Foundation of China(Nos.51522905,51379186)
文摘Nano particles have been found to be effective in enhancing many properties of regular concretes. However, there is little information on the effect of nano particles on shotcrete. In fact, if similar positive effect of nano particles can also appear in shotcrete, they will greatly benefit the wide application of shotcrete in more and more repair and strengthening of structures in civil engineering, especially in corrosive environments. In this study, through experiments on 70 specimens, the effects of nano SiO2, CaCO3 and Al2O3 particles on the early-age porosity, pore size distribution, compressive strength and chloride permeability of shotcrete were investigated.Test results indicated that nano SiO2 particles significantly increased the compressive strength and chloride penetration resistance; nano Al2O3 and CaCO3 particles had slight enhancing effect on the compressive strength; nano CaCO3 particles were most effective in promoting the chloride penetration resistance of shotcrete. As a conclusion, nano SiO2 particles were recommended when both early age compressive strength and chloride penetration resistance were crucial, and nano CaCO3 particles were recommended when only chloride penetration resistance was concerned for their high cost-effectiveness.
基金Supported by the Key Program of the National Natural Science Foundation of China (Grant No. 50438010)the Research and Application Programs of Key Technolo-gies for Major Constructions in the South-North Water Transfer Project Construction in China (Grant No. JGZXJJ2006-13)
文摘UHTCC (ultrahigh toughness cementitious composite), which is a kind of ultrahigh toughness cemen- titious composites material, exhibits pseudo strain hardening feature when subjected to tension load, and has enormous ductility and prominent crack dispersal ability. Accordingly, UHTCC can improve mechanical behavior of ordinary concrete structure especially its durability, and has been regarded as historical breakthrough to traditional cementitious materials. In this paper, the study focuses on flexure behavior of steel reinforced beam made of UHTCC. Based on the plane section assumption, along with two equilibrium equations of force and moment, the formulae to calculate the flexural load capability for the reinforced ultrahigh toughness cementitious composite (RUHTCC) beam were developed under the assumption that the compression stress- strain relationship in the UHTCC material is a bilinear model. Following this, the simplified formulae were further evolved by effective rectangle stress distribution approach in order to facilitate design of practical engineering. Two effective parameters introduced in effective rectangle approach were determined. The mathematical expressions to evaluate limited rein- forcement ratio, flexural stiffness as well as ductility index were proposed, too. Last, two series of dif- ferent reinforcement ratios of the RUHTCC beams were tested in four-point flexure loading. For com- parison purposes, ordinary RC (reinforced concrete) beams also were prepared. Both moment curva- ture curves and load mid-span displacement curves were recorded and compared with the theoretical calculations. A good agreement between them was found, which validates the proposed theoretical formulae. For ductility index, a slightly big difference between the experimental values and the calcu- lated ones exists. The experimental results show that, compared to control RC beams, the RUHTCC beam can improve both flexural capacity and ductility index, and the degree of improvement will de- crease with the increase in the reinforcement ratio. Particularly, the results also reveal that lager crack width in control beams can be greatly reduced by formation of tightly-spaced fine cracks in UHTCC, which offers more durable structures.
基金Supported by the Key Program of the National Natural Science Foundation of China(Grant No.50438010)the Research and Application Programs of Key Technolo-gies for Major Constructions in the South-North Water Transfer roject Construction in China(Grant No.JGZXJJ2006-13)
文摘Based on the concept of functionally graded concrete,UHTCC(ultrahigh toughness cementitious composites)material with excellent crack-controlling ability is strategically substituted for part of the concrete,which surrounds the main longitudinal reinforcement in a reinforced concrete member.Investigations on bending behavior of such a functionally graded composite beam crack-controlled by UHTCC(abbreviated as UHTCC-FGC beam)have been carried out.After establishing a theoretical cal-culation model,the paper discusses the results of four-point bending experiment on long composite beams without web reinforcement,and validates the theoretical formulae through experimental results of UHTCC-FGC beams with different thicknesses of UHTCC layer.Besides improving bearing capacity and saving steel reinforcements,the results indicate that UHTCC-FGC beams can also effectively control the deformation and enhance the ductility of members.At last,the optimal thickness of UHTCC layer in UHTCC-FGC beams has been confirmed,which can not only save materials and improve mechanical performance of members,but also be very effective in preventing corrosion-induced damage and enhancing the durability of members by controlling crack width below 0.05mm under service conditions.
