Effects of polypropylene twisted bundle fibers on the mechanical properties of high-strength oil palm shell lightweight concrete

In this study, the effects of a new type of non-metallic fiber (polypropylene twisted bundle (PPTB)) on the slump and mechanical properties of oil palm shell (OPS) concrete have been investigated. The results showed that increasing the volume fraction of PPTB fibers, it slightly decreases the workability and density of the concrete. It has found that the compressive strength of OPS concrete increases with increasing PPTB fiber volume fraction. The results revealed that the reinforcement of OPS concrete with steel and PPTB fibers reduces the strength loss of OPS concrete in poor curing environments. In addition, the fiber with low volume fraction (up to 0.25 %) is more efficient in improving the flexural strength of OPS concrete compared to its splitting tensile strength. The average modulus of elasticity (E value) is obtained to be 17.4 GPa for all mixes, which is higher than the values reported in previous studies and is within the range for normal weight concrete. The performance of the PPTB fibers is comparable to that for steel fibers at a volume fraction (V_f) of 0.5 %, which provides less dead load for lightweight concrete. The findings of this study showed that the PPTB fibers can be used as an alternative material to enhance the properties of OPS concrete. Hence, PPTB fibers are a promising alternative for lightweight concrete applications.     

A new method of producing high strength oil palm shell lightweight concrete

This paper presents a new method to produce high strength lightweight aggregate concrete (HSLWAC) using an agricultural solid waste, namely oil palm shell (OPS). This method is based on crushing large old OPS. Crushed OPS are hard and have a strong physical bond with hydrated cement paste. The 28 and 56 days compressive strength achieved in this study were about 53 and 56 MPa, respectively. Furthermore, it was observed that it was possible to produce grade 30 OPS concrete without the addition of any cementitious materials. Compared to previous studies, significantly lower cement content was used to produce this grade of concrete. Unlike OPS concrete incorporating uncrushed OPS aggregate, this study found that there is a strong correlation between the short term and 28-day compressive strength.     

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.     

A comparison study of the mechanical properties and drying shrinkage of oil palm shell and expanded clay lightweight aggregate concretes

For making artificial lightweight aggregate, selected raw materials are fed into a rotary kiln at high temperature. Providing such a high temperature is costly and generally, the process of making artificial lightweight aggregate is not environmentally friendly. The use of natural lightweight aggregate for making lightweight concrete can lead to low-cost construction. The use of a solid waste lightweight aggregate namely oil palm shell (OPS) as coarse aggregate, is not only environmentally friendly but leads to a low-cost material. This study is a comparison between some engineering properties of OPS lightweight concrete and an artificial lightweight (expanded clay) concrete with low water to cement ratio, along with having good workability and without any segregation. The test results show that OPS concrete has better mechanical properties and a higher efficiency factor than expanded clay lightweight concrete. The ceiling strength of expanded clay lightweight concrete occurs at an early age; while it happens in OPS concrete at a later age. The crack pattern of the tested specimens shows that OPS is much stronger than expanded clay. On the other hand, the compressive strength of OPS lightweight concrete is more sensitive to lack of curing. Although OPS lightweight concrete shows twice the amount of drying shrinkage than expanded clay lightweight concrete in the short term, this difference reduces significantly at later ages.     

Effect of steel fibres on mechanical properties of high-strength concrete

Steel fibre reinforced concrete (SFRC) became in the recent decades a very popular and attractive material in structural engineering because of its good mechanical performance. The most important advantages are hindrance of macrocracks’ development, delay in microcracks’ propagation to macroscopic level and the improved ductility after microcracks’ formation. SFRC is also tough and demonstrates high residual strengths after appearing of the first crack. This paper deals with a role of steel fibres having different configuration in combination with steel bar reinforcement. It reports on results of an experimental research program that was focused on the influence of steel fibre types and amounts on flexural tensile strength, fracture behaviour and workability of steel bar reinforced high-strength concrete beams. In the frame of the research different bar reinforcements (2∅6 mm and 2∅12 mm) and three types of fibres’ configurations (two straight with end hooks with different ultimate tensile strength and one corrugated) were used. Three different fibre contents were applied. Experiments show that for all selected fibre contents a more ductile behaviour and higher load levels in the post-cracking range were obtained. The study forms a basis for selection of suitable fibre types and contents for their most efficient combination with regular steel bar reinforcement.     

Assessment of factors influencing mechanical properties of steel fiber reinforced self-compacting concrete

In the last decade the steel fiber reinforced self-compacting concrete (SFRSCC) has been used in several partially and fully structural applications. This study investigates how the inclusion of steel fibers affects the properties of SFRSCC. For this purpose, an extensive experimental program including different cement contents of 400, 450 and 500 kg/m³, two maximum aggregate sizes of 10 and 20 mm along with steel fiber volume fractions of 0%, 0.38%, 0.64% and 1% was conducted. The water/cement ratio was kept constant at 0.45 for all the mixes studied. Mechanical properties were tested for compressive, splitting tensile and flexural strengths and modulus of elasticity. The results showed that mixture characteristics and volume fraction of steel fibers can significantly affect these major properties. Furthermore, this study represents extensive comparisons using database that have been gathered from a wide variety of international sources reported by many researchers and data obtained experimentally, which came up with about some discrepancies in the results.     

Effect of high volume fly ash on mechanical properties of fiber reinforced concrete

This paper reports the effects of incorporating high volume fly ash in fiber reinforced concrete. Fly ash was mixed as a partial fine aggregate replacement of approximately one third of the fines volume. The fibers were polypropylene or steel fibers at a maximum proportion of 1% by volume of the concrete. The results showed that fiber reinforced concrete that included high fly ash volume achieved compressive and tensile strength values that are more than double those of concrete without fly ash. Values of other mechanical properties have also achieved significant increase due to fly ash addition. It is suggested that a large quantity of fly ash is necessary to enhance the efficiency of fiber reinforcement. Polypropylene fibers resulted in gains up to 50% while steel fibers achieved gains up to more than 100%. This enhancement is believed to be due to the microstructural modification and densification in the transition zone between the matrix and the fibers.

---

Résumé Cet article décrit les effets de la cendre volante quand elle est incorporée, en grande quantité, à du béton enrobé de fibres. D'une part, la cendre volante est mélangée au béton de manière à remplacer le contenu en granulat fin qui équivaut à environ un tiers du volume des matériaux fins. D'autre part, le béton est enrobé de fibres, à base de polypropylène ou d'acier, dans une proportion maximale de 1% par volume de béton. Les résultats obtenus démontrent que, mélangé à une quantité volumineuse de cendre volante, le béton enrobé à l'aide de fibres offre, entre autres propriétés mécaniques, une résistance à des efforts de compression et de traction qui dépasse nettement le double de celle que l'on obtient avec du béton dépourvu de cendre volante. On en déduit qu'une grande quantité de cendre volante s'avère nécessaire pour améliorer l'efficacité du renforcement à base de fibres. En outre, l'utilisation de fibres de polypropylène permet d'atteindre une efficacité jusqu' à 50%, tandis que cette dernière excède 100% avec des fibres d'acier. Ces améliorations sont attribuées à la modification et à la densification microstructurelles qui ont lieu dans la zone de transition entre la matrice de béton et les fibres utilisées.

     

Effect of silica fume particle size on mechanical properties of short carbon fiber reinforced concrete

The addition of short carbon fibers (CF) in concrete leads to changes of both the mechanical and electrical properties of the hardened product. The addition of silica fume (SF) to concrete mixtures with CF facilitates an even distribution of fibers within the mixture volume and improves the strength and multifunctional properties of the product. In this work the influence of the particle size distribution of commercial SF on the strength properties of CF reinforced concrete has been studied. Also the influence of the addition of methyl-cellulose as a fiber dispersing agent that improves the homogeneity of the mixture has been studied. The results show a different behavior of concrete depending of the average SF particle size (between 1 μm and 60 μm). The evolution of the elastic compressive modulus of carbon fiber reinforced concrete (CFRC) is linked to the one of the compressive strength, with a good coincidence with the CEB (Comité Euro-International du Béton) formula values. This parameter is only slightly decreased by the addition of methyl-cellulose.     

Mechanical properties of lightweight ceramic concrete

Concrete produced using a magnesium phosphate binder can exhibit faster strength gain and result in lower overall environmental impacts than concretes produced with Portland cement binders. This paper reports a study to develop and characterize the rheological and mechanical properties of lightweight ceramic concretes (LWCC) that use a magnesium potassium phosphate binder. The aggregate type and the overall mix composition were primary variables in the study. Aggregate types included expanded clay, expanded slate, and expanded shale. Crushed bottom ash aggregate from a local coal-fired thermal generating station was also used. The aggregates of a given material varied by size fraction and by surface characteristics in some cases. The test results showed that increases in the water/binder ratio increased the slump flow but had negligible influence on the setting time. The compressive strength and density of the LWCCs both decreased with increases in the aggregate/binder mass ratio and the water/binder ratio, regardless of the type of lightweight aggregate. The 28 day compressive strength and density ranged from 17 to 36 MPa and 1600 to 1870 kg/m³ respectively. Regardless of the aggregate type, increasing the water/binder ratio also reduced the elastic modulus, modulus of rupture and direct shear strengths. Relationships were developed to directly relate these mechanical properties to the corresponding compressive strengths. The results indicate that LWCCs using a magnesium phosphate binder and lightweight aggregates can be formulated with rheological and mechanical properties suitable for structural applications.     

纳米SiO2对钢纤维/混凝土高温后力学性能及微观结构的影响

研究了掺纳米SiO2的钢纤维混凝土(NSFC)、钢纤维混凝土(SFRC)和普通混凝土(NC)三种材料在不同加热温度后的抗压、劈裂和抗折强度等力学性能,对不同温度热处理后的微观结构进行了SEM分析,对钢纤维与过渡区界面的相结构进行了XRD分析.结果表明:在测试温度范围内,NSFC的抗压、劈裂和抗折强度均高于SFRC和NC的强度,且在400℃时达到最大值.在常温下,NSFC的抗压、劈裂和抗折强度较NC分别提高27.01％、63.28％和54.12％,400℃高温热处理后比NC分别高35.09％、84.62％和87.23％; SEM分析表明,在钢纤维与过渡区的界面处,致密度提高,显微硬度提高.由于固相反应,使界面区结构发生变化,在钢纤维表层形成扩散渗透层(白亮层),即化合物层,呈锯齿状,XRD分析证明,白亮层主要由FeSi2和复杂的水化硅酸钙组成,从而增强了钢纤维与基体的粘结力,提高了混凝土的高温力学性能.     

Durability of steel embedded in structural lightweight concrete

Interim results of a long-term investigation on the durability of steel reinforcement embedded in expanded slate structural lightweight concrete are reported. The influence of concrete cover, cement content and of partial replacement of lightweight fines with natural sand was studied. Surface crazing was found to increase with cement content and increasing fine particles. The carbonation depth, and the relative permeability measured by alcohol absorption, were found to decrease with increasing cement content. Inclusion of natural sand in the mix reduced the permeability and the penetration of the carbonation front into the concrete. No instance of damage due to corsosion was found in embedded steel reinforcement after two year's exposure to industrial atmosphere.     

钢纤维增韧微膨胀钢管混凝土界面粘结性能研究

进行了30根钢纤维微膨胀钢管混凝土试件推出试验,系统研究了核心混凝土与管壁的界面粘结性能,阐述了推出试验过程中试件界面粘结破坏特征,并对界面粘结性能的影响因素进行了分析。结果表明,钢纤维微膨胀钢管混凝土界面粘结强度较普通钢管混凝土明显提高。径厚比和含钢率是钢纤维微膨胀钢管混凝土界面粘结强度的主要影响因素。钢纤维的掺加导致微膨胀钢管混凝土界面粘结性能降低,其体积掺量建议不宜超过0.75%。含钢率达到22%时,钢纤维掺量与界面长度对界面粘结性能影响不明显。     

Mechanical and thermal properties of prepacked aggregate concrete incorporating palm oil fuel ash

Prepacked aggregate concrete (PAC) is a special type of concrete which is made by placing coarse aggregate in a formwork and injecting a grout either by pump or under the gravity force to fill the voids. Use of pozzolanic materials in conventional concrete has become increasingly extensive, and this trend is expected to continue in PAC as well. Palm oil fuel ash (POFA) is one of these pozzolanic ash, which has been recognized as a good pozzolanic material. This paper presents the experimental results of the performance behaviour of POFA in developing physical and mechanical properties of prepacked aggregate concrete. Four concrete mixes namely, prepacked concrete with 100% OPC as a control, and PAC with 10, 20 and 30% POFA were cast, and the temperature growth due to heat of hydration and heat transfer in all the mixtures was recorded. It has been found that POFA significantly reduces the temperature rise in prepacked aggregate concrete and delay the transfer of heat to the concrete body. The compressive and tensile strengths, however, increased with replacement up to 20% POFA. The results obtained and the observation made in this study suggest that the replacement of OPC by POFA is beneficial, particularly for prepacked mass concrete where thermal cracking due to extreme heat rise is of great concern.     

Effect of fiber arrangement on mechanical properties of short fiber reinforced composites

The present paper developed a three-dimensional (3D) “tension–shear chain” theoretical model to predict the mechanical properties of unidirectional short fiber reinforced composites, and especially to investigate the distribution effect of short fibers. The accuracy of its predictions on effective modulus, strength, failure strain and energy storage capacity of composites with different distributions of fibers are validated by simulations of finite element method (FEM). It is found that besides the volume fraction, shape, and orientation of the reinforcements, the distribution of fibers also plays a significant role in the mechanical properties of unidirectional composites. Two stiffness distribution factors and two strength distribution factors are identified to completely characterize this influence. It is also noted that stairwise staggering (including regular staggering), which is adopted by the nature, could achieve overall excellent performance. The proposed 3D tension–shear chain model may provide guidance to the design of short fiber reinforced composites.     

Influence of process parameters on the strength of oil palm kernel shell pellets

In this study, the influence of processing and storage parameters on the strength of oil palm kernel shell pellets was determined. The strength of the pellets increased with compaction pressure but pelletizing pressures above 188 MPa had little effect on the pellet strength. At these high pressures, the pellets achieved no or near-zero porosities, indicating that the maximum strength was achieved. The diametrical tensile strengths of the pellets were much weaker than the compressive strengths when compacted at the same compaction pressure. The pellet strengths were found to increase with longer hold times during the compaction process. This was due to a continuous decrease in porosities until near-zero porosities were achieved, when increasing the hold time no longer led to further strengthening of the pellets. The time-dependent characteristic of the pellet strength was also reflected in the reduction in strength as compaction speed was increased. The strength of the pellets decreased significantly after 1 day (24 h) of storage, with a higher decrease observed when the pellets were stored under a higher humidity condition. These changes during storage could create difficulties during handling and transportation and may affect gasification performance.     

Effect of electromechanical hardening on the mechanical properties of carbon steel

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, No. 3, pp. 26–30, May–June, 1989.     

Mechanical properties of steel fibre reinforced lightweight concrete with pumice stone or expanded clay aggregates

This paper presents basic information on the mechanical properties of steel fibre-reinforced light-weight concrete, manufactured using pumice stone or expanded clay aggregates. Results are presented for standard compressive tests and indirect tensile tests (splitting tests on cylinder specimens and flexure tests on prismatic beams using a three-point loading arrangement) under monotonically increasing or cyclically varying loads. The influence of steel fibres and aggregate types on modulus of elasticity, compressive and tensile strength and post-peak behaviour is evaluated. Test results show that compressive strength does not change for pumice stone aggregates, while an increase is observed for expanded clay; tensile strength and fracture toughness are significantly improved for both pumice stone and expanded clay. The results also show that with both expanded clay and pumice stone lightweight aggregates a suitable content of fibres allows one to obtain performances comparable with those expected from normal weight concrete, the important advantage of lower structural weight being maintained.     

Effect of aggregate shape on the mechanical properties of a simple concrete

The influence of aggregate shape on the fracture energy, tensile strength and elasticity modulus in concrete is considered. For this purpose, eight simple cement-based composites were designed, manufactured and tested, with two purposes: to provide experimental data that can throw some light on this involved problem and help in the design of future cement-based composites, and supply information that can be used as a benchmark for checking numerical models of concrete failure, as this simple composite is amenable to being modelled quite easily. Thirty-six notched beams were tested and values of the fracture energy and elasticity modulus were recorded. The tensile strength was measured from indirect standard tensile tests. Comparison with available experimental data is also included and discussed. Fracture was modelled using a cohesive crack with a bilinear softening function; data of the softening function inferred from the experimental measurements are also provided and discussed.