Equivalent Flexural Strength Ratio Research Articles

Engineering properties and fracture behaviour of high volume palm oil fuel ash based fibre reinforced geopolymer concrete

This article reports investigation carried out using high volume palm oil fuel ash (POFA-90%) based geopolymer concrete using oil palm shell (OPS) as coarse aggregate. The tensile and fracture properties of OPS based lightweight geopolymer concrete (OPSGC) with the addition of steel fibres (SF) of two aspect ratios (AR80, AR65) and three volume fractions (0.25%, 0.50%, 0.75%) were investigated. The results were compared with that of normal weight geopolymer concrete (NWGC) with and without steel fibre of AR80 and AR65 (0.50% volume fraction). The higher values of flexural and splitting tensile strengths of OPSGC could be attributed to stronger bond between the rougher surfaces of the crushed OPS and matrix. The addition of SF(AR80) produced higher splitting strength, flexural strength and total fracture energy of 5%, 6% and 50–80%, respectively compared to the corresponding values of SF(AR65). The toughness and equivalent flexural strength ratio of OPSGC were found higher than the corresponding values of NWGC and this could be attributed to the ductility of OPS. The values of residual load and residual strength in two-deflection limits of L/600 and L/150 indicated the progressive failure, which reflected the ductility of the OPSGC with fibres.

Investigation of Mechanical Properties of Steel Fibre- Reinforced Concrete

Steel fibre-reinforced concrete (SFRC) is widely used in the structural elements of buildings: industrial floors, slabs, walls, foundation, etc. When a load is applied to a fibre- reinforced composite consisting of a low-modulus matrix reinforced with high-strength, high- modulus fibres, the plastic flow of the matrix under stress transfers the load to the fibre; this results in high-strength, high-modulus material which determines the stiffness and stress of the composite. In this study the equivalent flexural strength, equivalent flexural ratio Re,3 and the compressing strength of SFRC are investigated. Notched test specimens with five different dosages of steel fibres (20, 25, 30, 35, 40 kg/m3) were prepared using industrial concrete. Determination of flexural tension strength was carried out according to the EU norm EVS-EN 14651:2005+A1:2007. The equivalent flexural strength and subsequent equivalent flexural ratio Re,3 of SFRC with a dosage of 20, 25, 30, 35 kg/m3 similar to their average values and with a dosage of 40 kg/m3 were 31% higher than their average values. The compressive strength of the steel fibre-reinforced concrete was slightly higher compared to plain concrete, except specimens with the dosage of 40 kg/m3 where the increase was 30%.

Flexural Strength Characteristics of Compacted Cement-Polypropylene Fiber Sand

An improvement of flexural strength of cement stabilized sand using polypropylene fibers designated as compacted cement-polypropylene fiber-sand (CCFS) is investigated in this research. The studied material performance of the CCFS includes postpeak behavior, toughness, and equivalent flexural strength ratio. The fiber inclusion significantly improves the postpeak flexural behavior, which is a requirement for bound pavement materials. The first peak flexural strength f1 and stiffness of both compacted-cement-sand (CCS) and CCFS are essentially the same for the same cement content. For low fiber content, the fiber inclusion primarily prevents the sudden failure. The CCFS exhibits deflection-hardening behavior and the peak flexural strength (fp) is higher than the first peak flexural strength (f1) for medium to high fiber contents. Two modes of failure are noted: single failure plane and stress transfer–induced multiple cracks. For low to medium fiber contents, the single failure plane is observed for both deflection-softening and deflection-hardening behaviors. The high fiber contents of 2% can significantly distribute the load to different parts of the test beam; hence, multiple cracks are observed even at a large failure deflection, without a clear single failure plane. The fiber inclusion has been proven as suitable for the bound pavement CCFS material in both the failure mode and the flexural properties. These improvements are of practical significance in pavement performance and design.

Flexural performance of fibre reinforced concrete made with steel and synthetic fibres

The ductility of concrete made with commercially available steel and synthetic fibres has been investigated. Flexural stress–deflection relationships have been used to determine: flexural strength, flexural toughness, equivalent flexural strength, and equivalent flexural strength ratio. The flexural toughness of concrete was found to increase considerably when steel and synthetic fibres were used. However, equal dosages of different fibres did not result in specimens with the same flexural toughness. Flexural toughness differences of almost 35J existed even at the same fibre dosage. This also resulted in considerable differences in the minimum required ground supported slab thickness.

Use of steel and polypropylene fibers to improve flexural performance of deep soil–cement column

In this study, steel and polypropylene fibers are used to improve flexural performance of soil–cement pile. Deep cement mixing (DCM) technique has been used for decades in Thailand to improve the strength of soft clay in Bangkok and vicinity. However, since it is made of about 10–20% of cement, it also shares similar properties as the harden cement such as good compressive strength, low permeability, and poor tensile and flexural strengths (brittle). In several occasions when subjected to bending moment caused by horizontal loadings (induced by large embankment), the poor flexural strength can lead to a failure of the soil–cement column. In order to improve its flexural strength and brittleness, a technique of mixing short fibers (similar to that used in conventional concrete) is introduced to the soil cement mixture. Two types of fiber are used to produce the fiber reinforced soil cement (FRSC): polypropylene and steel fibers at three different volume fractions of 0.5%, 0.75% and 1.0%. Flexural performance of the FRSC is carried out according to ASTM C1609. Results show improvements in the flexural performance as seen by the increase in the equivalent flexural strength ratio and the residual strength when the fibers are incorporated into the mix. The polypropylene fiber is found to perform better than the steel fibers. With the increasing volume fraction, the toughness is also increase.

Polypropylene Fiber Reinforced Concrete for Rigid Airfield Pavement

The effect of adding polypropylene fibers; with different shapes and volume fractions; on the compressive strength, modulus of rupture, load-deflection curve and flexural toughness (equivalent flexural strength ratio) of concrete was investigated. Crimped and twisted polypropylene fibers were used with 0.0%, 0.2%, 0.4% and 0.6% volume fractions. It was found that the compressive strength, flexural strength and the equivalent flexural strength ratio of concrete increased about 11%, 25% and 40% respectively by adding 0.6% volume fraction of twisted polypropylene fiber. In addition; it was found that the contribution of polypropylene fiber to the flexural strength and flexural toughness was more effective when twisted polypropylene fiber was added comparing to crimped polypropylene fibers. The experimental results were used in numerical example using FAARFIELD program to explore the airfield pavement thickness reduction resulted from polypropylene fiber incorporation.

Simplified method for concrete pavement design with discrete structural fibers

The addition of discrete macro fibers to plain concrete increased the flexural capacity of concrete slabs supported on ground. Flexural strength tests (i.e., ASTM C78) did not capture the added toughening mechanisms fibers imparted to concrete slabs. Based on the results of small and large-scale testing, the equivalent flexural strength ratio ( R e,3) was used to quantify the increased flexural capacity of synthetic and steel-fiber reinforced concrete slabs over plain concrete slabs. An effective flexural strength approach was proposed for the design of fiber-reinforced concrete pavements. The method applied a percentage increase to the modulus of rupture (MOR) of plain concrete based on the measured R e,3 value for the fiber-reinforced concrete mixture. The effective MOR accounts for the contribution of fibers to the added slab flexural capacity and fits into existing linear elastic-based design guidelines for concrete pavement. Large-scale test results verified the proposed design approach for fiber-reinforced concrete pavements. The proposed method is applicable for concrete mixtures reinforced with relatively low volume fractions of fibers that produce R e,3 values between 20% and 50%. Such fiber concrete mixtures are practically and economically attractive as they can be mixed, placed, and compacted with normal paving techniques.