Early-age load resistance of fibre reinforced shotcrete linings

Widespread interest has developed into early-age strength development for fibre reinforced shotcrete (FRS) and its influence on the time to safe re-entry immediately after spraying. Cycle times for drive development within mines, and in civil tunnel construction, can strongly depend on the time to safe re-entry and this, in turn, affects excavation progress rates and overall project economy. The majority of research into safe re-entry times has focused on strength development in hardening shotcrete under the assumption that toughness, adhesion to the rock surface, and the ability of the FRS lining to support unstable ground are all related to the strength of the concrete matrix. Although anecdotal evidence supporting this assumption has been gathered through observations of satisfactory ground control at mines utilizing FRS for ground support, ad hoc evidence alone cannot be used as a basis for rational estimation of safe re-entry times. Instead, the present investigation has sought to quantify the parameters that influence early-age FRS lining capacity and develop an engineered approach to shotcrete lining design and estimation of safe early-age re-entry times through a rational assessment of load resistance.     

The impact resistance of masonry units bound with fibre reinforced mortars

The seismic rehabilitation of stone masonry buildings requires a quantitative understanding of the constituent materials under variable rates of loading. The stress-rate sensitivity of cementitious composites and rock has been intensively investigated. However, the literature on the impact resistance of masonry joints is scarce, particularly with regard to the bond behaviour using fibre reinforced mortars. This paper describes the stress-rate sensitivity of masonry units bound with fibre reinforced Type S mortars. A drop-weight impact machine was used to generate stress rates in the range of 1 kPa/s–10⁸ kPa/s. The dynamic impact factor and stress-rate sensitivity were evaluated for the flexural strength of the mortar and the bond strength and further, the pattern of failure was noted for each mix and loading rate. Polypropylene micro-fibres were incorporated as discrete reinforcement at 0%, 0.25% and 0.5% volume fraction into the mortar. Results show that the impact resistance of the masonry units increased in the presence of fibres. However, the stress-rate sensitivity of the bond strength decreased with an increase in the fibre content. Also, where as the mode of failure in those masonry units bound with plain mortars was through fracture at the mortar-block interface, the addition of fibres transferred the failure plane to within the masonry block.     

The use of fibre reinforced polymers to improve seismic resistance of masonry

Fibre reinforced polymers (FRPs) constitute a class of advanced composite materials which have the potential to change significantly masonry rehabilitation and strengthening. Their light weight means that they do not alter the mass of a structure and thus the inertial forces from seismic excitation. Their strength and, in the case of sprayed glass FRP, their toughness, indicate that they can alter the load deformation response considerably for the better. Further testing is required, but FRP’s open an exciting new line of possibilities for masonry.     

碳纤维水泥基复合材料功能响应的机理研究

碳纤维水泥基复合材料能以电信号输出的形式反映自身受力状况和内部的损伤程度.通过单丝拔出的细观力学试验,研究了荷载作用下碳纤维水泥基复合材料电阻率变化的机理,获得了水泥基碳纤维复合材料界面电阻随界面力的变化规律.水泥基单丝试样电阻的变化可归纳为由3个方面的原因引起:一是由于纤维-基体之间界面脱黏导致导电网络的变化;二是由于纤维-基体之间界面结构变化而引起导电网络发生改变;三是碳纤维在拉伸应力的作用下其自身电阻会增大,由这一因素引起的电阻变化所占比例极小.复合材料内部导电网络发生改变,导致其电阻率发生变化,材料具有感知应力、应变的功能特性.在循环载荷的作用下,试样电阻率的变化规律与载荷的变化规律显示出了良好的一致性.     

Evaluating the ductility and shear behaviour of carbon fibre reinforced polymer and glass fibre reinforced polymer reinforced concrete columns

Brittle shear failure in short reinforced concrete (RC) columns has been identified as one of the most dangerous failure modes that may cause collapse of bridges, based on research findings and damage reconnaissance of past earthquakes. Using ABAQUS software, the effect of carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) on retrofitting of existing circular RC columns, and also enhancing of shear strength have been studied. Five types of concrete columns were studied in the ‘as built’ condition to investigate the shear failure mode of columns. These columns were assessed again after being retrofitted by using CFRP and GFRP. Based on findings of this research, the effect of CFRP jackets on improving the shear behaviour of column is more than that of GFRP jackets, while GFRP jackets are more effective than CFRP jackets, regarding their contribution in increasing the column ductility. Therefore, these FRP composites can be utilized in different conditions, according to column demand for increasing the ductility or shear strength. Copyright © 2010 John Wiley & Sons, Ltd.     

碳纤维水泥基复合材料导热系数的研究

研究了碳纤维含量对水泥基复合材料导热系数的影响.试验结果表明:由于碳纤维加入水泥基材料中的同时也引入了气泡,导热系数随着碳纤维含量的增加而降低,碳纤维含量小于1.0%时,下降的幅度较大;含量大于1.0%时,下降的幅度变缓.通过对试验数据拟合得到了导热系数随碳纤维含量变化的函数关系.     

椰壳纤维增强水泥基复合材料综合性能研究

以水泥和砂为基体相,以椰壳纤维为增强相,制备椰壳纤维增强轻质水泥基复合材料.研究配合比和沸煮处理综合影响下椰壳纤维增强水泥基复合材料的密度以及抗弯强度和抗压强度性能.研究结果表明,椰壳纤维作为轻质增强相在建筑结构轻质墙体填充材料方面具有一定的研究价值和较好的应用前景.     

椰壳纤维增强水泥基复合材料力学性能研究

制备椰壳纤维增强水泥基复合材料,分析其物理和力学性能,结果表明:材料抗压强度随椰壳含量增加下降幅度较大,而抗弯强度下降不明显,并出现假塑性破坏的断裂特征,指出该材料在轻质填充材料上具有一定的工程应用前景。     

Influence of geometric factors on the punching load resistance of early-age fibre reinforced shotcrete linings

Understanding the early-age properties of fibre reinforced shotcrete (FRS) is critical to the accurate estimation of the time to safe re-entry under freshly sprayed FRS linings. Previous research in the field has indicated that shear failures dominate early-age load resistance and thereby govern the performance of a lining during the first few hours after spraying. This investigation has examined the influence of several geometric variables on shear resistance in a punching mode of failure. In particular, the research has addressed the influence of the size, shape, eccentricity, and inclination of punching loads on the apparent shear strength of an early-age fibre reinforced shotcrete (FRS) lining.     

玻璃纤维增强水泥基复合材料耐水性能的研究

文章研究了掺加外加剂和聚合物乳液对玻璃纤维增强水泥基复合材料耐水性能的影响。通过分析实验数据,发现同时掺加适量的外加剂A和聚合物乳液K,可以显著提高玻璃纤维增强水泥基复合材料的耐水性能。     

Assessment of wheat fibre reinforced cementitious matrix

The technology of using synthetic fibres in reinforced concrete structures continues to mature. This research is intended to address the use of natural fibres derived from wheat straws for reinforcing cementitious matrix specimens. In order to study the properties of the cementitious matrix reinforced with wheat fibres, 156 specimens were tested in uniaxial compression and flexure. The compression tests were conducted on 2 in (50.8 mm) cubes, while the flexural tests were conducted on 1.58 × 1.58 × 6.30 in (40 × 40 × 160 mm) prisms. Several lengths of fibres and percentages in the range of 0.5% to 5% by volume of the specimens were tested in order to determine which would yield the highest load and stiffness. Specimens reinforced with polypropylene fibres were tested in order to benchmark the results. The average uniaxial compression load of the specimens reinforced with 0.5% long wheat fibres exceeded that of their counterparts reinforced with 0.5% polypropylene fibres by 15%.     

Performance of thermally damaged fibre reinforced concretes

Mechanical characteristics of Fibre Reinforced High Performance Concrete (FR-HPC) subjected to high temperatures were experimentally investigated in this paper. Three different concretes were prepared: a normal strength concrete (NSC) and two High Performance Concretes (HPC1 and HPC2). Fibre reinforced concretes were produced by addition of steel or polypropylene fibres in the above mixtures at dosages of 40 kg/m³ and 5 kg/m³, respectively. A total of nine concrete mixtures were produced and fibres were added in six of them. At the age of 120 days specimens were heated to maximum temperatures of 100, 300, 500 and 700 °C. Specimens were then allowed to cool in the furnace and tested for compressive strength, splitting tensile strength, modulus of elasticity and ultrasonic pulse velocity. Reference tests were also performed at air temperature (20 °C). Residual strength of NSC and HPC1 was reduced almost linearly up to 700 °C and 500 °C, respectively whereas the residual strength of HPC2 was sharply reduced up to 300 °C. Explosive spalling was observed on both HPC. Addition of steel fibres increased the residual strength up to 300 °C, but spalling still occurred in HPC1 and HPC2. Such an explosive behavior was not observed when polypropylene fibres were added in the mixtures; however, in this case the residual mechanical characteristics of all concretes were significantly reduced.     

Mechanical behaviour and fibre dispersion of hybrid steel fibre reinforced self-compacting concrete

In this study, mixture design, workability, fibre dispersion/orientation, mechanical properties and fracture behaviour of hybrid steel fibre reinforced self-compacting concretes (HSFRSCCs) were investigated. Three different types of steel fibres with and/or without hooked-ends were added to the mixtures in two different volume fractions (0.75 and 1.5% of the total volume of concrete). The results of slump flow, U-box, V-funnel and J-ring tests have shown that increasing the fibre content of the concretes slightly reduced the workability of HSFRSCC, and the main influencing factor on flowability is the geometry of fibres. The addition of fibres, although did not change the final flowability, decreased the rate of flowability. The results from the experimental tests showed that the flexural strengths increased slightly with increasing strength of long fibres, whereas the splitting tensile strength remained unchanged. The concretes with high strength, long steel fibres show behaviour of enhanced toughness and ductility compared to that with normal strength steel fibres. The orientation and distribution of fibres in concrete have been investigated by image analysis and it was observed that fibres dispersed homogeneously in all concrete series without any clumping. With increasing the amount of fibres, the fibres were more vertically orientated relative to the bending loading direction, resulting in enhancement in the mechanical properties of concrete.     

Plant fibre reinforced cement components for roofing

Composites of blast furnace slag (BFS) based cement mortar reinforced with vegetable fibres are presented. Roofing components are produced with these composites through a simple and low-energy consuming method, including ordinary vibration and curing in a wet chamber. Composites reinforced with eucalyptus pulp, coir fibres and with a mixture of sisal fibre and eucalyptus pulp gave a suitable performance, with compressive strength higher than 20 MPa and modulus of rupture (MOR) higher than 3 MPa. The performance of tiles made with these composites is in accordance with international requirements, with maximum load higher than 450 N, in wet conditions.     

Gridshell structures in glass fibre reinforced polymers

Applications in which composite materials are used as bearing structural elements are rare and generally copy structural solutions that have been optimized for steel for years. Unfortunately these materials have very different properties, therefore specific construction methods and specific structural forms have to be invented for composite materials. Gridshell structures may be one of those. So, after a brief history of gridshells, a demonstration with the Ashby’s method that glass fibre reinforced polymers are an alternative for this kind of structure is shown. An original experimental test for the identification of the parameters of the short and long time behaviours of bent pultruded tubes is then detailed. Afterwards a scale one prototype of composite gridshell is presented and loaded. Results of the experimental tests are compared to numerical results of a non-linear analysis done with the dynamic relaxation method. The authors then concluded on the feasibility of such composite gridshells and on their potential for future development.     

纤维砂浆增强预应力锚索锚固效果的研究

边坡加固中经常采用预应力锚索,足够的锚固力是保证边坡稳定性的重要条件。灌浆材料的性能直接影响到锚索锚固力的稳定性和耐久性。在砂浆中掺入一定配比的聚丙烯纤维,通过室内模型试验和现场试验,证明纤维的掺入可以提高锚固段与围岩的粘结力,在依托工程中应用纤维砂浆达到了良好的加固效果,并采用弹塑性有限元方法模拟锚索的工作过程,研究表明这种纤维砂浆能够改善锚固段的受力变形特征,增强砂浆的抗裂性,提高锚索的锚固能力。     

Strength and permeability of steel fibre reinforced grouts

The feasibility of using steel fibres to improve the tensile strength and durability of cement–sand grout was investigated. Initial tests focused on achieving pumpable grout mixes and 13 mm round steel fibres with a diameter of 0.16 mm were found to be compatible with a conventional grout paddle mixer and piston pump. Subsequently, grouts with 0.5% and 1% fibre volume fraction were subjected to compressive and splitting tensile strength tests, coefficient of permeability tests and wet–dry cycles. The effect of partial cement replacement with silica fume and blast furnace slag was also investigated. It was found that steel fibres were beneficial for short- and long-term tensile strength. Coefficient of permeability was not adversely affected by addition of fibres. Resistance to microcracking and increase in permeability after wet–dry cycles was also improved by steel fibres. Partial replacement of cement with blast furnace slag resulted in enhanced mechanical properties, whereas the results for silica fume were mixed.     

Sound insulation of fibre reinforced mud brick walls

The aim of this paper is to find a better alternative for the insulation of industrial noise and to improve the mechanical properties of fibre reinforced mud bricks. It was observed that the fibre reinforced mud bricks fulfill the compressive strength and sound insulation requirements of the ASTM and Turkish Standards. Basaltic pumice as an ingredient was found to improve the sound insulation performance of fibre reinforced mud bricks. The experimental results showed that fibre reinforced mud brick, with basaltic pumice as ingredient, can be used in industrial buildings for walls to improve sound insulation.     

Flexural capacity of thin wall fibre reinforced cement

A method of calculating the flexural strength (cracking) of fibre reinforced cement floor and wall systems is presented. The method for flexural strength is based on non-linear stress-strain relationship at failure tension and corresponding stress distribution in section at cracking and subsequent failure. The method is verified in tests of full-scale ‘V’ and ‘U’ shaped panels made of asbestos-cement which were tested as simply supported beams designed for the construction of low cost housing and wall facades. Additional tests were performed on small sized samples to verify the mechanical properties of material used.     

聚丙烯纤维增强膨胀混凝土试验研究

通过正交试验，研究2种聚丙烯纤维、4种膨胀剂分别在4个掺量和2个水胶比水平下，对混凝土工作性、力学性能和收缩变形特性的影响。研究表明，聚丙烯纤维和微膨胀剂复合，能提高混凝土的抗折强度、降低抗折弹性模量，并补偿收缩；聚丙烯纤维、膨胀剂和减水剂协同作用对混凝土力学性能的改善优于膨胀剂的单一作用。