Modelling basalt fibre reinforced glass concrete slabs at ambient and elevated temperatures

The analysis of tests conducted on small-scale slabs at ambient and elevated temperatures is presented in this paper. The slabs were produced from a new type of concrete containing different levels of glass sand and basalt fibre. Two methods were used for this purpose: a simplified method developed previously and a finite element method, using the software package ABAQUS. For the slabs at ambient temperature, the results showed a good correlation for the load–displacement relationship between the test and the two models up to the failure loads. For the slabs at elevated temperature, the ABAQUS model gave a reasonable prediction for the temperature–displacement relationship while the simplified method gave a conservative prediction for the maximum allowable vertical displacement. As a result, the simplified method underestimated the temperature at which the reinforcement fracture occurs for this type of concrete slab, incorporating glass sand and basalt fibres. Further work is required to remove this conservatism from the simplified design method for this type of concrete.     

Full-scale test of a pile supported steel fibre concrete slab

The aim of the short-term studies is to investigate the structural behaviour of pile supported slabs made of steel fibre concrete (SFC) only and combined reinforced steel fibre concrete. The studies include tests on an elevated slab where a combination of reinforcement bars and steel fibres have been used in one half of the slab and SFC only in the other half. The tests were performed on a column-supported elevated slab that simulates a half scale model of an industrial pile-supported floor slab. The short-term tests showed considerable structural and crack arresting performance that also increased with a higher dosage of fibres. A small addition of conventional reinforcement bars further increased the ultimate load capacity P _Max. P _Max was in the range of 125–298 kN for the two types of slab. The results indicate that SFC can be used with verifiable results in structural applications for elevated slabs and pile-supported floor slabs despite that the material testing from the ordered SFC showed a larger scatter in properties and that the calculated load capacities were only 40–220 kN. Main causes of deviance are arch and membrane effects.     

Properties of glass concrete reinforced with short basalt fibre

Experimental work was carried out to develop information about the properties of glass aggregate concrete reinforced with chopped basalt fibre. Recycled waste mixed colour glass was used as a partial replacement (20%, 40%, and 60% by weight) for the natural fine aggregate with different volume fractions of fibre (0%, 0.1%, 0.3%, and 0.5% by total mix volume). The combined effect of the glass and the basalt fibre on the mechanical properties of the fresh and hardened concrete was investigated. The heat transfer through the thickness for this type of concrete was also investigated. A statistical analysis was also carried out to investigate the variance of the data for each mix. The test results and the statistical analysis indicated that there is a slight reduction in the compressive and splitting tensile strength with the increase in the glass content above 20%. Using basalt fibre leads to an enhancement in it for all mixes and there is an optimum content of fibre in each percentage of glass sand which gives higher strength. A slight decrease in the heat transfer through the concrete specimens was also observed.     

Investigation of thermo-mechanical properties of adhesive used for bonding CF fabrics to concrete members using post-curing techniques

Carbon fibre reinforced polymers (CFRPs) have been increasingly employed for structural strengthening using bonding adhesives. The work in this paper reports the use of post-curing temperature on adhesive properties in CFRP/concrete systems which use a bonding adhesive under a sustained load to achieve thermal and mechanical performance. An increase in the adhesives glass transition temperature were achieved for post-curing, and as expected it was found that the improvement in the glass transition was greater for samples post-cured at high temperatures, compared to those which had only been exposed to moderately elevated temperatures. However, the single-lap shear test results at elevated temperatures under sustained loads showed a greater improvement in the bond-loss temperature compared with those which were post-cured at only moderately elevated temperatures, with higher temperatures negatively affecting the concrete properties, particularly at the adhesive/concrete interface.     

Investigation of thermo-mechanical properties of adhesive used for bonding CF fabrics to concrete members using post-curing techniques

Carbon fibre reinforced polymers (CFRPs) have been increasingly employed for structural strengthening using bonding adhesives. The work in this paper reports the use of post-curing temperature on adhesive properties in CFRP/concrete systems which use a bonding adhesive under a sustained load to achieve thermal and mechanical performance. An increase in the adhesives glass transition temperature were achieved for post-curing, and as expected it was found that the improvement in the glass transition was greater for samples post-cured at high temperatures, compared to those which had only been exposed to moderately elevated temperatures. However, the single-lap shear test results at elevated temperatures under sustained loads showed a greater improvement in the bond-loss temperature compared with those which were post-cured at only moderately elevated temperatures, with higher temperatures negatively affecting the concrete properties, particularly at the adhesive/concrete interface.     

The thermal behaviour of glass fibre investigated by thermomechanical analysis

A thermomechanical analysis (TMA) procedure has been developed with the capability of probing the thermal behaviour of glass fibre. A single glass fibre was successfully mounted into TMA fibre configuration and several thermomechanical programmes were carried out over a wide temperature range from 20 to 900 °C. It was found that measured coefficient of linear thermal expansion of boron-free E-glass fibre remained constant below 300 °C and the values had an excellent agreement with that found in the literature. At higher temperatures an abrupt length change in glass transition region allowed for the determination of glass transition temperature. The results from isothermal measurement showed significant fibre length shrinkage, which was a function of both temperature and time. It follows that there exist two mechanisms, thermal expansion and structural relaxation, which together account for overall thermomechanical responses of glass fibre. The former is related to the decrease of Young’s modulus at elevated temperatures and the latter is considered responsible for the observed increase of room-temperature Young’s modulus after thermally conditioning glass fibre at various temperatures.     

Effect of partial replacement of sand by fine crumb rubber on impact load behavior of concrete beam: experiment and nonlinear dynamic analysis

The effect of partial replacement of sand by fine crumb rubber on the impact load performance of concrete was investigated experimentally and numerically. Specimens were prepared for 5, 10 and 20 % replacements by volume of sand. For each case, three beams of size 400 × 100 × 50 mm were loaded to failure in a drop-weight impact machine by subjecting it to 20 N weight from 300 mm height, and similar beams were tested under static load. In both cases, the load–displacement and fracture energy were studied. The dynamic beam behavior was also analyzed numerically using the finite-element method based LUSAS V.14 software. It was found that, the impact tup, and inertial and bending loads increased with increase of sand replacement by fine crumb rubber, while the static peak bending load always decreased. The rubberize concrete was stronger and more energy-absorbing under impact loading, than under static loading.     

Variation of strength and stiffness of fibre reinforced polymer reinforcing bars with temperature

This paper presents the results of tensile mechanical properties of FRP reinforcement bars, used as internal reinforcement in concrete structures, at elevated temperatures. Detailed experimental studies were conducted to determine the strength and stiffness properties of FRP bars at elevated temperatures. Two types of FRP bars namely: carbon fibre reinforced polyester bars of 9.5 mm diameter and glass fibre reinforced polyester bars of 9.5 mm and 12.7 mm diameter were considered. For comparison, conventional steel reinforcement bars of 10 mm and 15 mm diameter were also tested. Data from the experiments was used to illustrate the comparative variation of tensile strength and stiffness of different types of FRP reinforcing bars with traditional steel reinforcing bars. Also, results from the strength tests were used to show that temperatures of about 325 °C and 250 °C appear to be critical (in terms of strength) for GFRP and CFRP reinforcing bars, respectively. A case study is presented to illustrate the application of critical temperatures for evaluating the fire performance of FRP-reinforced concrete slabs.     

Fire structural resistance of basalt fibre composite

Basalt fibres are emerging as a replacement to E-glass fibres in polymer matrix composites for selected applications. In this study, the fire structural resistance of a basalt fibre composite is determined experimentally and analytically, and it is compared against an equivalent laminate reinforced with E-glass fibres. When exposed to the same radiant heat flux, the basalt fibre composite heated up more rapidly and reached higher temperatures than the glass fibre laminate due to its higher thermal emissivity. The tensile structural survivability of the basalt fibre composite was inferior to the glass fibre laminate when exposed to the same radiant heat flux. Tensile softening of both materials occurred by thermal softening and decomposition of the polymer matrix and weakening of the fibre reinforcement, which occur at similar rates. The inferior fire resistance of the basalt fibre composite is due mainly to higher emissivity, which causes it to become hotter in fire.     

风积砂地基装配式基础下压水平力组合荷载试验

根据塔克拉玛干沙漠腹地2 个装配式基础的现场试验,分析了下压与水平力组合荷载作用下风积砂地基装配式基础的变形、结构受力特性以及地基土压力变化规律,并采用Veisc 理论计算了下压与水平力组合荷载作用下风积砂地基的极限承载力。结果表明,在下压水平力组合荷载作用下:1) 风积砂地基装配式基础顶部竖向和水平方向的位移值相差不大。基础顶部竖向沉降主要由支架压缩量和地基沉降量组成,在极限荷载工况时,角钢支架变形量为风积砂地基沉降量的2 倍~3倍,最终是由于地基的水平承载力不足而使得基础丧失承载能力;2) 角钢支架处于压弯受力状态,在破坏荷载时,尚未达到角钢屈服应力,也未出现压曲失稳;3) 风积砂地基装配式基础的承载性能与基础底板混凝土板条的排列方式有关,平行于混凝土板条轴线方向的水平承载能力高;4) 可采用Vesic理论计算风积砂地基装配式基础在倾斜荷载作用下的竖向下压极限承载力。     

Study of Abrasive Wear Volume Map for PTFE and PTFE Composites

The potential of this work is based on consideration of wear volume map for the evaluation of abrasive wear performance of polytetrafluoroethylene (PTFE) and PTFE composites. The fillers used in the composite are 25% bronze, 35% graphite and 17% glass fibre glass (GFR). The influence of filler materials, abrasion surface roughness and applied load values on abrasive wear performance of PTFE and PTFE composites were studied and evaluated. Experimental abrasive wear tests were carried out at atmospheric condition on pin-on-disc wear tribometer. Tests were performed under 4, 6, 8 and 10 N load values, travelling speed of 1 m/sec and abrasion surface roughness values of 5, 20 and 45 μm. Wear volume maps were obtained and the results showed that the lowest wear volume rate for PTFE is reached using GFR filler. Furthermore, the results also showed that the higher is the applied load and the roughness of the abrasion surface, the higher is the wear rate. Finally it is also concluded that abrasive wear process mechanism include ploughing and cutting mechanisms.     

Mechanical performance of composite-strengthened concrete structures

The interest of using fibre reinforced plastic (FRP) materials in rehabilitating damaged concrete structures respectively has been increased rapidly in recent years. In this paper, the structural behaviours of the glass–fibre composite strengthened concrete structures subjected to uni-axial compression and three point bending tests are discussed through experimental studies. Two types of concrete structure are used in present study, they are concrete cylinder and rectangular concrete beam. Discussion on the environmental effects of composite strengthened reinforced concrete (RC) structures is also addressed. Experimental results show that the use of glass–fibre composite wrap can increase the load carrying capacity of the plain concrete cylinders with and without notch formation. The flexural load capacity of the concrete beam increases to more than 50% by bonding 3 layers of glass–fibre composite laminate on the beam tension surface. Direct hand lay up method gives better strengthening characteristic in term of the ultimate flexural load compared with pre-cured plate bonding technique. The flexural strengths of composite strengthened RC beams submerged into different chemicals solution for six months are increased compared with the RC beams without strengthening. The strength of the concrete structure is seriously attacked by strong acids.     

Crack growth resistance in fibre reinforced alkali-activated fly ash concrete exposed to extreme temperatures

This paper examines the crack growth resistance of alkali-activated fly ash concrete under extreme temperatures. Plain and hybrid fibre reinforced alkali activated concrete prepared with fly ash were subjected to a range of temperatures from ? 30 to 300 °C, sustained for 2 h. The alkali activation was effected with a blend of sodium hydroxide and sodium silicate. A fibre blend of steel to polypropylene in the volume ratio of 4:1 and a total as high as 1% by volume fraction reinforced the mixtures. The resulting systems were examined for residual strength under compression and splitting tension. Further, notched prisms were loaded under 4-point flexure to evaluate the residual fracture toughness. Based on the results, four different stages for fracture behaviour were identified with superior fibre efficiency seen at sub-zero temperatures. Across the breadth of temperatures examined, adding fibres led to higher residual fracture toughness for those systems that displayed a narrow range of thermal conductivity.     

Comparison of compressive and splitting tensile strength of autoclaved aerated concrete (AAC) containing water hyacinth and polypropylene fibre subjected to elevated temperatures

This paper described the results of an extensive experimental study on the comparative between compressive and splitting tensile behavior of autoclaved aerated concrete (AAC) containing water hyacinth fibre (WHF) with AAC mixed with polypropylene (PP) fibre. The specimens of AAC-WHF and the AAC-PP were subjected to elevated temperatures (100, 200, 400, 800 and 1000 °C). Test results indicated that an optimum water hyacinth and PP fibre dosage was at 0.5 and 0.75 % by volume respectively. The maximum residual in compressive strength and the splitting tensile strength of AAC-WHF and AAC-PP were 0.43 and 0.16 N/mm² and 0.51 and 0.18 N/mm² respectively. In addition, the loss in residual strength of AAC mixed PP fibre was slower than AAC mixed WHF. The splitting tensile strength of AACs was more sensitive to high temperatures than the compressive strength. A severe strength loss was observed for all of the AAC after exposure to 800 °C. Based on the test results, it can be concluded that the addition of PP fibers can significantly promote the residue mechanical properties of AAC during heating.     

Fracture properties of concrete reinforced with steel–polypropylene hybrid fibres

This research discusses polypropylene fibres and three sizes of steel fibres reinforced concrete. The total fibre content ranges from 0% to 0.95% by volume of concrete. A four-point bending test is adopted on the notched prisms with the size of 100×100×500 mm³ to investigate the effect of hybrid fibres on crack arresting. The research results show that there is a positive synergy effect between large steel fibres and polypropylene fibres on the load-bearing capacity and fracture toughness in the small displacement range. But this synergy effect disappears in the large displacement range. The large and strong steel fibre is better than soft polypropylene fibre and small steel fibre in the aspect of energy absorption capacity in the large displacement range. The static service limitation for the hybrid fibres concrete, with “a wide peak” or “multi-peaks” load–CMOD patterns, should be carefully selected. The ultimate load bearing capacity and the crack width or CMOD at this load level should be jointly considered in this case. The K_IC and fracture toughness of proper hybrid fibre system can be higher than that of mono-fibre system.     

高温下钢筋混凝土板抗冲击性能及其影响因素

钢筋混凝土(RC)结构在遭受火灾作用时,常会由于楼层坍塌而继发冲击作用,对楼板产生高温与冲击的耦合作用。该文同时考虑高温热力耦合效应和冲击荷载作用下的应变率效应,开展了高温下RC板抗冲击性能研究。通过分别将RC板抗火和抗冲击的试验结果与模拟结果进行对比,验证了该文所建立模型的正确性。分析获得了RC板在不同受火时间和不同能量冲击荷载作用下的动力响应,讨论了板厚和配筋率对高温下RC板抗冲击性能的影响。结果表明：火灾高温作用将显著影响RC板的抗冲击性能。随着受火时间的增加,RC板的冲切破坏损伤更加严重,RC板的跨中峰值位移也更大。板厚的增加能明显改善RC板的高温下的抗冲击性能,而配筋率的增加对RC板在高温下的抗冲击性能的影响有限。     

Shear capacity of steel and polymer fibre reinforced concrete beams

This paper deals with the application of a plasticity model for shear strength estimation of fibre reinforced concrete beams without stirrups. When using plastic theory to shear problems in structural concrete, the so-called effective strengths are introduced, usually determined by calibrating the plastic solutions with tests. This approach is, however, problematic when dealing with fibre reinforced concrete (FRC), as the effective strengths depend also on the type and the amount of fibres. In this paper, it is suggested that the effective tensile strength of FRC can be determined on the basis of the tensile stress-crack opening relationship found from wedge splitting tests. To determine the effective compressive strength of FRC, it is proposed to adopt the formula used for conventional concrete and modify it by introducing a fibre enhancement factor to describe the effect of fibres on the compressive softening behaviour of FRC. The enhancement factor is determined as the ratio of the areas below the stress–strain curves for FRC and for conventional concrete. The outlined approach has been verified by shear testing of beams containing no fibres, 0.5% steel fibre volume and 0.5% polymer fibre volume. The tests results are compared with estimations and show satisfactory agreements, indicating that the proposed approach can be used.     

Tribological performance of polymer composites used in electrical engineering applications

Sliding wear performance of 20% mica-filled polyamide 6 (PA6 + 20% mica) and 20% short glass fibre-reinforced polysulphone (PSU + 20 GFR) polymer composites used in electrical applications were investigated using a pin-on-disc wear test apparatus. Two different disc materials were used in this study. These are AISI 316 L stainless steel and 30% glass fibre-reinforced polyphenylenesulphide (PPS + 30%GFR) polymer composite. Wear test was carried out at 10, 20 and 30 N applied load values and 0·5 m/s sliding speed and at ambient temperature and humidity. Different combinations of rubbing surfaces were examined and friction coefficient and specific wear rate values were obtained and compared. For two material combinations used in this investigation, the coefficient of friction shows insignificant sensitivity to applied load values and large sensitivity to material combinations. For specific wear rate, PA6 + 20% mica composite has shown insensitivity to change in load, speed and materials combination while PSU + 20% glass fibre composite has shown high sensitivity to the change in load and material combinations. The friction coefficient of PA6 + 20% mica and PSU + 20 glass fibre rubbing against the AISI 4140 steel disc is between 0·35 and 0·40. In rubbing against PPS + 30% glass fibre their values were between 0·25 and 0·30. Specific wear rate for PA6 + 20% mica and PSU + 20% glass fibre composites are in the order of 10^???13 to 10^???14 m²/N. Finally, the wear mechanisms are a combination of adhesive and abrasive wear processes. In terms of application, especially in electrical systems, a substantial contribution was provided to extend switch life. Thus, besides robustness, this also ensured safety for the system and the users against undesirable situations.     

Prediction of steel fibre reinforced concrete under flexure from an inferred fibre pull-out response

Steel fibre-reinforced concrete (SFRC) is being used in a variety of structural applications, yet there is still considerable debate how to express and evaluate flexural toughness for design purposes. This is holding back the material's development as a permanent structural material. Existing beam and slab test methods have problems with variability or their application in structural design. Furthermore, existing models of SFRC flexural behaviour do not fully capture what happens at the cracked section in terms of the fibre-matrix interactions. Typical of these approaches is the modelling of the tension zone from single fibre pull-out tests, which is problematic in measurement of the load-displacement relationship, the interaction of groups of fibres and the extensive testing required to cover all permutations of fibre geometry. An alternative approach is proposed where the average pull-out response of the fibres bridging the cracked zone is inferred from flexural beam tests. The characteristic load versus crack-mouth opening displacement behaviour for a particular fibre concrete then forms part of the stress and strain/displacement profile in a flexural analysis to predict moment capacity in a design calculation. The model is explained together with its validation by comparing the predicted load-displacement response for a range of fibre volumes in sprayed and cast SFRC. It is concluded that the analysis of beam load/deflection curves to infer the fibre pull-out response is a viable approach. It offers a promising solution to the need for a flexural design model combined with a practical method of characterizing the tensile contribution of steel fibres.