Flexural strength of palm oil clinker concrete beams

This paper presents an experimental program on the flexural behaviour of reinforced concrete beams produced from palm oil clinker (POC) aggregates. POC is obtained from by-product of palm oil milling. Utilisation of POC in concrete production not only solves the problem of disposal of this solid waste but also helps to conserve natural resources. An experimental work was conducted involving eight under-reinforced beams with varying reinforcement ratios (0.34–2.21%) which were fabricated and tested. The data presented include the deflection characteristics, cracking behaviour and ductility indices. It was found that although palm oil clinker concrete (POCC) has a low modulus of elasticity, the test results revealed that the deflection of singly reinforced POCC beams, with reinforcement ratio less than 0.524, under the design service load is acceptable as the span-deflection ratios range between 250 and 257 and these values are within the allowable limit provided by BS 8110. In addition, the results reported in this paper indicate that the BS8110 based design equations can be used for the prediction of the flexural capacity of POCC beams with reinforcement ratio up to 2.23%.     

Shear strength of palm oil clinker concrete beams

This paper presents experimental results on the shear behavior of reinforced concrete beams made of palm oil clinker concrete (POCC). Palm oil clinker (POC) is a by-product of palm oil industry and its utilization in concrete production not only solves the problem of disposing this solid waste but also helps to conserve natural resources. Seven reinforced POCC beams without shear reinforcement were fabricated and their shear behavior was tested. POCC has been classified as a lightweight structural concrete with air dry density less than 1850 kg/m³ and a 28-day compressive strength more than 20 MPa. The experimental variables which have been considered in this study were the POCC compressive strength, shear span–depth ratio (a/d) and the ratio of tensile reinforcement (ρ). The results show that the failure mode of the reinforced POCC beam is similar to that of conventional reinforced concrete beam. In addition, the shear equation of the Canadian Standard Association (CSA) can be used in designing reinforced POCC beam with ρ ⩾ 1. However, a 0.5 safety factor should be included in the formula for ρ < 1.     

基于细观模拟的轻骨料混凝土动态压缩破坏及尺寸效应分析

为研究冻融后自密实轻骨料混凝土单轴压缩下的声发射(AE)特性,对未掺引气剂的自密实轻骨料混凝土试件进行0次、50次、100次快速冻融试验。结果表明：随着冻融次数增加,试件轴压应力-应变曲线趋于完整,峰值应力有明显降低;声发射峰值频率主要位于15 kHz~45 kHz, 85 kHz~105 kHz, 235 kHz~255 kHz和285 kHz~320 kHz 这4个“优势频段”区间,对应于混凝土内部预存裂纹或孔隙压密,骨料/砂浆界面增强层的开裂,粗骨料断裂破坏以及砂浆的开裂。受冻后的试件在轴压作用经历拉伸裂缝与剪切裂缝之间的交替转化,最终形成主裂缝导致破坏。冻融作用以及应力水平变化对AE信号源分布有较大影响,随着应力水平的增加,AE信号源趋于活跃,且在试样断裂面有聚集趋势。     

Advantages of mortar-based design for coloured self-compacting concrete

The development of coloured self-compacting concrete (C-SCC) opens new fields of application, since it adds attractive alternatives for challenging architectural designs in terms of shapes and colour, to the already versatile aesthetic characteristics of traditional coloured concrete. The benefits of using cement paste or mortar tests as a previous step in SCC design to optimize mixture proportions have been recognized. This paper shows the advantages of using a mortar-based mix design methodology for C-SCC. In addition to rapid and easy determination of the proportions of the mixtures including different types of pigments, cements, mineral additions, and chemical admixtures, the mortar approach enables observation of the effect of pigments on the viscosity of C-SCC and evaluation of specific aspects as the colorimetric parameters, the colour homogeneity and the surface finishing.     

Concrete mix design for high strength self-compacting concrete using metakaolin

Metakaolin is a highly reactive pozzolanic admixture and has got significant potential for the development of concrete composites such as High Strength High Performance Concrete (HSHPC) and self compacting concrete (SCC), if appropriately designed. However, for obtaining the required performance in any of these concrete composites, metakaolin should be properly proportioned so that the resulting concrete would satisfy both the strength and performance criteria requirements of the structure. The present work is an effort towards obtaining a new mix methodology for the design of high strength self compacting metakaolin concretes based on the efficiency concept. The methodology has been successfully verified through a proper experimental investigation and the self compacting metakaolin concretes were evaluated for their self compactability and strength characteristics. The results indicate that the proposed method can be capable of producing high strength SCC of about 120 MPa.     

Mix design and fresh properties for high-performance printing concrete

This paper presents the experimental results concerning the mix design and fresh properties of a high-performance fibre-reinforced fine-aggregate concrete for printing concrete. This concrete has been designed to be extruded through a nozzle to build layer-by-layer structural components. The printing process is a novel digitally controlled additive manufacturing method which can build architectural and structural components without formwork, unlike conventional concrete construction methods. The most critical fresh properties are shown to be extrudability and buildability, which have mutual relationships with workability and open time. These properties are significantly influenced by the mix proportions and the presence of superplasticiser, retarder, accelerator and polypropylene fibres. An optimum mix is identified and validated by the full-scale manufacture of a bench component.     

Impact of particle packing mix design method on fracture properties of natural and recycled aggregate concrete

The fracture properties of four types of concrete prepared using natural coarse aggregate and recycled coarse aggregate and conventional and particle packing method (PPM) of mix design approaches are studied. The three‐point bending (TPB) test is performed using three different sizes of single edge notched beam. The fracture energy is calculated from the load‐CMOD curve obtained in the TPB test, and in this process the load‐CMOD curve is curtailed at 2% of the depth of the beam. Based on CTOD_c and w₁ relationship, appropriate softening function is used to estimate the double‐K fracture parameters. The fracture energy and fracture toughness parameters of recycled aggregate concrete (RAC) is inferior to the natural aggregate concrete (NAC). The PPM mix design improves the fracture properties of concrete in comparison to the conventional mix design approach. The fracture properties of PPM mix designed RAC are comparable to that of NAC prepared using conventional method.     

Effect of the mix design on the robustness of fresh self-compacting concrete

Self-compacting concrete (SCC) has many advantages compared to vibrated concrete. A disadvantage is the lower robustness of fresh SCC. SCC is more sensitive to small changes in the mix design, material properties, and the applied production methods. In an experimental program, the influence of important mix design parameters on the robustness of SCC was studied. First, the influence of the paste volume and the water-to-powder volumetric ratio was investigated. Depending on the mechanisms providing stability in the mixture, different levels of impact were observed. When the yield stress is the main factor providing stability in the mixture, a change in the water content will mainly affect the yield stress, making the stability of the yield stress the most important factor determining the robustness of the mixture and can be improved by lowering the paste volume. Analogue, the sensitivity of the plastic viscosity is determining the robustness of mixtures in which mainly the plastic viscosity is providing stability. The robustness of such a mixture can be improved by increasing the water-to-powder volumetric ratio. The influence of two types of viscosity modifying agents (VMA's) on the robustness of fresh SCC was examined in a second stage. The two used VMA's (diutan gum and attapulgite clay) were especially effective in SCC mixtures having a high yield stress and a low plastic viscosity. In mixtures having a low yield stress and a high plastic viscosity, the inclusion of a VMA in the mix design resulted in a decrease of the robustness.     

Feret coefficients for white self-compacting concrete

Several tests on white mortar, micro-concrete, concrete and self-compacting concrete, considering different additions and admixtures, were conducted to characterize white cement and determine the corresponding Feret coefficients. It was concluded that: (1) it is possible to make different mixtures of white self-compacting concrete (WSCC) with the materials adopted; (2) the method suggested by the JSCE is the one that better adapts to the studied WSCC mixtures; (3) the obtained values for the Feret coefficients can help the concrete designer predicting the compressive strength of the WSCC; (4) the Feret coefficients for WSCC are different from those for regular, white or gray, concrete.1359-5997 © 2005 RILEM. All rights reserved.     

Comparison of particle packing models for proportioning concrete constitutents for minimum voids ratio

This paper reports the findings of a study of four particle packing models used to proportion the mix constituents (solid particles) of concrete to produce a minimum voids ratio (or maximum packing density). The models have been compared using laboratory tests and published data. The basic mathematics of the models is discussed, particularly how each model defines the particle size distribution of the solid particles. The models have been applied to both the aggregate (sand and gravel) and the cement phase (PC, PFA, GGBS and limestone fines) and the estimated voids ratio compared with that measured in the laboratory. It was found that the models give broadly the same output and suggest similar combinations of materials to give the minimum voids ratio. Using the materials considered it was found that the largest improvement in voids ratio was achieved with the aggregate phase. The particle sizes of the cements considered here were similar and, as a result, only small improvements in voids ratio could be achieved. It was noted that proportioning concrete mix constituents to minimise voids ratio did tend to produce a harsher mix than normal. However, using the mix suitability factor, proposed by Day (1999), reduced this problem. There are some detail differences between the models suggesting further refinements could be carried out and a modification to one of the models is provided.     

Mix design of concrete for prestressed concrete sleepers using blast furnace slag and steel fibers

The application of ground granulated blast furnace slag (GGBFS) and steel fibers in prestressed concrete railway sleepers was investigated in this study. The use of GGBFS was considered as an eco-friendly material aimed at reducing CO₂ emissions and energy consumption as well as to enhance the durability performance of railway sleepers. Steel fibers improves the durability and structural performance in terms of crack control and reduction of spalling and can replace shear reinforcement. The mix proportions of the concrete incorporating GGBFS (56% GGBFS) and GGBFS with steel fibers (56% GGBFS and 0.75% steel fibers) were determined through a series laboratory tests and a life cycle assessment. These mixes satisfied the requirements of the Korean Railway Standard and resulted in improved flexural capacity as well as less CO₂ emissions compared with current railway sleepers. Using these mixes, a total of ninety prestressed concrete sleepers were produced in a factory under the same manufacturing process as current railway sleepers, and their mechanical properties as well as durability performance were evaluated. The mix with partial replacement of Type III Portland cement by GGBFS showed an improved resistance to chloride ion penetration and freeze-thaw cycles compared with the concrete used for current railway sleepers. However, these mixes were more vulnerable to carbonation. The mix with GGBFS and steel fibers (mix BSF) showed a slightly better durability performance than the mix with GGBFS only (mix BS), including better carbonation and freeze-thaw resistances. The mix BSF showed decreased chloride ion penetration depth than mix BS but showed a slightly higher chloride ion diffusion coefficient.     

Random particle model for concrete based on Delaunay triangulation

In this paper, an efficient simulation method for obtaining a random particle model for concrete is outlined. First, the ‘take-and-place method’ and its extension, the ‘directed searching process’, are discussed briefly and the shortcomings are indicated. A new method, the ‘divide-and-fill method’, appears to be more convenient, especially when only a small computer is used. In this simulation method the available space (two-dimensional) is divided in separate areas, using a Delaunay triangulation. These areas are filled with particles taking into account a given grading curve and gravel content. Comparison with physical concrete sections, obtained by means of image analysis, shows that the results of this method closely represent reality. The divide-and-fill method also yields a finite-element mesh in a quasi-automatic way.     

Torsional behaviour of steel fibre-reinforced oil palm shell concrete beams

The increasing demand for curved structural members has prompted an increase in the research on the torsional behaviour of concrete. Recently, oil palm shell (OPS) has received considerable attention as a material that enables the production of sustainable lightweight concrete. This work investigated the effects of steel fibre of 0.25%, 0.50%, 0.75% and 1.00% volume fractions on the mechanical properties and torsional resistance of OPS concrete (OPSC) and OPS fibre-reinforced concrete (OPSFRC) beams. The experimental results showed that the increase in fibre content resulted in better mechanical properties and torsional resistance of OPSFRC. The compressive, splitting tensile and flexural strengths of OPSFRC with 1% steel fibres were found to be 40%, 110% and 150%, respectively, higher than the control mix. The crack bridging effect also improved the pre-cracking and post-cracking torsional behaviour of OPSFRC. The highest cracking torque, ultimate torque, twist at failure and torsional toughness of 8.3 kNm, 8.5 kNm and 1.31 kNm/m were obtained for the mix with 1% steel fibre. Moreover, the crack arrest ability of the steel fibre reduced the primary torsional crack widths and formed multiple fine cracks. Further, a simplified torsional model is proposed to predict the torsional behaviour of OPSC and OPSFRC.     

Effects of heat treatment on oil palm shell coarse aggregates for high strength lightweight concrete

In this study, the effects of heat treatment on oil palm shell (OPS) coarse aggregates are evaluated for high strength lightweight concrete (HSLWC). OPS coarse aggregates are subjected to heat treatment at two temperature settings (60 and 150 °C) and duration of heat treatment (0.5 and 1 h). The reduction in density is found to be within the range of HSLWC when heat-treated OPS aggregates are added into the oil palm shell concrete (OPSC). The results reveal that workability of the OPSC increases with an increase in temperature and duration of heat treatment of the OPS aggregates. It is found that the maximum achievable 28-days and 90-days compressive strength is 49 and 52 MPa, respectively. Furthermore, the ultrasonic pulse velocity (UPV) is examined and the results showed that a good condition is achieved for the OPS HSLWC at the age of 3 days. The average modulus of elasticity (i.e. (E) value), is found to be 15.9 GPa for all mixes, which is higher than that reported in previous studies and is within the range of normal weight concrete. Hence, the findings of this study are of primary importance as they reveal that the selection of a suitable temperature and duration of heat treatment for OPS aggregates can be used as a new eco-friendly alternative method to enhance HSLWC.     

Evolution of alkaline activated ground blast furnace slag–ultrafine palm oil fuel ash based concrete

The two locally available pozzolanic solid wastes (PMs) – ultrafine palm oil fuel ash (UPOFA) and ground blast furnace slag (GBFS) – have been used as base materials to develop high alkaline activated strength concrete. The samples were prepared with combined aggregate modulus of 3.66 and at constant GBFS/PM that varied from 0 to 0.3. The combined alkaline activators (CAA) (Na₂SiO₃ and NaOH) to PMs ratios (CAA/PMs), temperature and curing durations also varied as 0.45–0.55, 25–90 °C, and 6–24 h, respectively. The findings revealed that the strength at 3-day and 28-day were 69.13 and 71.2 MPa, respectively and the respective optimum GBFS/PM, CAA/PM, temperature and curing duration are 0.2, 0.5, 60 °C and 24 h. GBFS was found to contribute to the soluble Ca, heterogeneity, and amorphousity of the product. This eventually facilitated the formation of suspected calcium-silicate-hydrate and the geopolymer products of Ca/Na-aluminosilicate-hydrate (C/NASH) that enhanced the compressive-strength results.     

Mix design method for self compacting metakaolin concrete with different properties of coarse aggregate

This study deals with a proposed mix design method for SCC utilizing different properties of coarse aggregate. The work was conducted in three phases, i.e. paste, mortar and concrete to facilitate the mix design process. Initial investigation on cement paste determined the basis for water cement ratio and superplasticizer dosage for the concrete. For the study on mortar, metakaolin (MK) as pozzolan was used at replacement levels of 5%, 10%, 15%, and 20% by weight of cement. Self compactability of mortars was obtained by adding suitable materials such as mineral admixtures and superplasticizer which provided a sufficient balance between flowability and viscosity of the mix. The optimum MK replacement level for cement was 10% from the viewpoint of workability and strength. Flowability of mortar decreased with the use of metakaolin. Moreover, strength of mortar increased when the optimum replacement level of pozzolan was used. Different fresh concrete tests were adopted. The results obtained for fresh concrete properties showed that flowability of concrete increased with increase flowability of mortar. The mixes which contained coarse aggregate with lower volume, small size, and continuous grading affected positively the fresh properties of SCC. Finally, the mix design method used was successful in producing SCC with different coarse aggregate properties.     

基于声发射技术的非标准自密实混凝土三点弯曲梁动态断裂特性

对不同初始缝高比的自密实混凝土(Self-compacting concrete,SCC)非标准三点弯曲梁开展不同加载速率下的断裂试验,获得其断裂的荷载-裂缝嘴张开口位移曲线及峰值荷载、断裂韧度、临界缝高比增量、弹性模量和柔度系数等断裂参数,结合Pearson相关性检验公式及加载速率效应模型,定量分析初始缝高比、加载速...     

Effect of steel fiber on the mechanical properties of oil palm shell lightweight concrete

This paper reports the results of a study conducted to investigate the effect of low volume content of steel fiber on the slump, density, compressive strength under different curing conditions, splitting tensile strength, flexural strength and modulus of elasticity of a grade 35 oil palm shell (OPS) lightweight concrete mixture. The results indicate that an increase in steel fiber decreased the workability and increased the density. All the mechanical properties except the modulus of elasticity (E) improved significantly. The 28 day compressive strength of steel fiber OPS lightweight concrete in continuously moist curing was in the range of 41–45 MPa. The splitting tensile/compressive and the flexural/compressive strength ratio for plain OPS concrete are comparable with artificial lightweight aggregate. The (E) value measured in this study was about 15.5 GPa on average for all mixes, which is higher than previous studies and is in the range of normal weight concrete. Steel fiber can be used as an alternative material to reduce the sensitivity of OPS concrete in poor curing environments.