Nabil M. Al-Akhras

Effect of wheat straw ash on mechanical properties of autoclaved mortar

This study investigates the effect of wheat straw ash (WSA) on the mechanical strength of autoclaved mortar. The mechanical properties studied include compressive, tensile, and flexural strengths of mortar. Mortar mixes were prepared using natural silica, wadi (local sand), and crushed limestone fine aggregates at a w/c ratio of 0.6. Mortar specimens were exposed to autoclave for 2.5 h at a pressure of 2 MPa. Three percentages of WSA replacement levels (3.6%, 7.3%, and 10.9%) by weight of sand were utilized in the study. The study showed that the replacement of sand by WSA increases the mechanical strength of autoclaved mortar. Mortar specimens containing limestone aggregate with 10.9% WSA replacement level showed an average increase in compressive, tensile, and flexural strength by 87%, 67%, and 71%, respectively, compared to control mortar specimens. Scanning electron micrographs for autoclaved paste specimens containing 7.3% WSA replacement level revealed a more packed structure compared to control paste specimens.

Influence of heat treatment on the behavior of clayey soils

Abstract This study examines the effect of temperature under laboratory conditions of three clayey soils collected from northern Jordan. Soils were subjected to four temperature levels, i.e. 100, 200, 300 and 400 °C. Various soil properties were studied including Atterberg limits, particle size distribution, optimum water content, maximum dry density, swelling potential, and unconfined compressive strength. Experimental results revealed that heat treatment higher than 100 °C resulted in a decrease in liquid and plastic limits, optimum water content, unconfined compressive strength, and swelling pressure of soils tested. However, maximum dry density increased slightly with an increase in temperature to reach a maximum value of 14.3 kN/m 3 at 400 °C for soil-1 compared to 12.9 kN/m 3 at ambient temperature. Heating the clayey soils at 400 °C decreased the liquid limit, plastic limit, optimum water content, swelling pressure, and unconfined compressive strength by 80%, 100%, 65%, 94%, and 100%, respectively, in average compared to soil specimens at ambient temperature.

Nondestructive Testing Procedure to Evaluate the Load-Carrying Capacity of Concrete Anchors

AbstractConcrete anchors are extensively used in the construction industry. Their applications range from erecting permanent objects such as sign poles, direction signs, lighting poles, and so on, to temporary support structures. Several destructive testing equipment types exist in the industry that can be used to evaluate the load-carrying capacity of concrete anchors. However, no nondestructive testing method has been proposed that can estimate their load-carrying capacity. This study develops a new relationship between the pull-out load-carrying capacity, P, of concrete anchors and Schmidt hammer rebound value, R. It was observed from experimentation that the load-carrying capacity of the concrete anchors depends on the embedment length, anchor diameter, concrete strength, and anchor alignment. The effect of anchor alignment was also observed during experimentation, and anchors with ill alignment of more than 5% can lead to lower load-carrying capacity. In addition, it is also possible to identify the ...

Flexure strengthening of lightweight reinforced concrete beams using carbon fibre-reinforced polymers

A series of 40 lightweight reinforced concrete (LWRC) beams of 1400 mm length and a rectangular cross section of 150 × 200 mm were cast, strengthened and then tested under four-point bending test to study the effectiveness of using externally applied carbon fibre-reinforced polymer (CFRP) composites as a method of increasing the flexural strength of under-reinforced LWRC beams. Parameters investigated include reinforcement ratio, ρ; ρ = 0.55ρb and ρ = 0.27ρb, CFRP sheet length; 600, 800 and 1000 mm, CFRP sheet width; beam width and half-beam width. Three types of strengthening schemes were used: jacketing covers the beam from bottom and two sides with total width of 500 mm, sheets at the tension side with width equal to beam width and sheets with width equal to half-beam width. Test results showed a limited increase in ultimate load-carrying capacity accompanied with some reduction in mid-span deflection for the strengthened beams. Among the strengthening schemes investigated, jacketing was the most effective for strength enhancement (about 41%) with respect to control beam; however, it reduced ductility significantly. An analytical model was proposed for predicting the ultimate load-carrying capacity of LWRC beams strengthened with CFRP composites.

The Durability of Partially-Damaged Concrete with the Addition of Silica Fume and Ground Granulated Blast Furnace Slag

This study investigates the durability of partially-damaged concrete with the addition of Silica Fume and Ground Granulated Blast Furnace Slag. Portland cement was replaced by 10% SF and 60% of GGBFS as a replacement of Portland cement. Thirty-six concrete cylinders (100 x 200 mm) were subjected to three compressive loading levels (50%, 75%, and 90% of its ultimate strength capacity). After 28 days of curing, the concrete specimens were experimentally tested for electrical resistivity, rapid chloride penetration (RCPT) and chloride migration coefficient (Dnssm) according to NT-BUILD 494. The experimental results showed that the GGBFS improves significantly the durability of concrete with the highest electrical resistivity and lowest chloride permeability compared to control and SF concrete and both SF and GGBFS had significant effect the concrete durability properties even when the concrete was subjected to compressive damage up to 90% of the compressive strength. A correlation between Dnssm and RCPT in partially damaged concrete was observed and an empirical linear relationship was developed to estimate Dnssm.

Evaluation of shear-deficient lightweight RC beams retrofitted with adhesively bonded CFRP sheets

A series of twenty-two shear-deficient lightweight reinforced concrete (LWRC) beams were casted and tested under four-point flexural loading to investigate the structural behaviour of shear-deficient LWRC beams retrofitted with adhesively bonded carbon fibre reinforced polymers (CFRP) sheets. The variables investigated in the study include as follows: shear-span to effective-depth ratio and different retrofitting schemes. The overall response of the LWRC beams, the onset of cracking, crack development and ductility were investigated. The experimental results indicated that the contribution of the CFRP to restore the shear capacity of the shear-deficient LWRC beams was significant. The ultimate shear strength of the retrofitted LWRC beams increased significantly (23–96%) depending on the technique used. The use of the CFRP transformed the mode of failure of some LWRC beams into a more ductile flexural one. The most effective technique for enhancing the shear capacity of the LWRC beams was the CFRP jacketing, followed by the U-strips, inclined strips, and side strips, respectively. The dominant failure mode for the retrofitted LWRC beams was the CFRP debonding from the beams surface by shearing of the concrete skin. An analytical model was developed and showed good correlation with the test results of this investigation.

Destructive and Nondestructive Testing on Silica Fume Concrete

Factors such as poor design, bad workmanship and a harsh environment can combine to cause deterioration within a concrete structure leading to visually unacceptable surface cracking or spalling of concrete cover [. In aggressive environments, corrosion of steel reinforcing bars is responsible for major deteriorations in concrete structures. Reduction in bar diameter leads to a lower resistance, which can result in brittle failure of the bar. Initiation and progression of reinforcing steel corrosion can lead to progressive weakening of the structure due to damage accumulation over a period of time, or in sudden catastrophic failures, such as the Berlin Congress Hall, a parking garage in Minnesota [. Antonaci et al. [ conducted an experimental study on different concrete cylinders damaged in compression followed by means of linear and nonlinear ultrasonic methods. Arndt et al. [ tested a concrete slab representing typical bridge decks in order to evaluate the ability of NDT methods to detect different phases of corrosion progression in concrete. Reinforced concrete beam-shaped samples were tested by Aveldano and Ortega [ in order to characterize concrete cracking due to reinforcing corrosion under different environments. Shah and Ribakov [ performed nonlinear ultrasonic testing of cubic concrete specimens with different frequency transducers. Al-Amoudi et al. [ investgated the relatioship between compressive strength of ordinary concrete and blended cement concrete with durability propeties of concrete samples and conculded that the addition of blended cement will improve the performance of concrete in ressiting corrosion of reinforcement. The main objective of this study is to investigate the effectiveness of using nondestructive testing to assess the performance of different types of concrete such as OPC and SFC. Also, to correlate different types of nondestructive testing and to investigate the possibility of capturing the occurrence of corrosion in reinforcing bars in concrete.

Strengthening of lightweight reinforced concrete slabs using different techniques

The present study examines the potential of using four different techniques in repairing and strengthening of preloaded, cracked, lightweight, reinforced concrete one-way solid slabs. Nineteen lightweight reinforced concrete (LWRC) slabs specimens were casted with one-third scale dimensions from prototype structure in buildings. The slabs dimensions were 1.2 m in length and cross section of (70 × 500) mm in depth and width. The slabs were reinforced with 3φ10 for the main reinforcement and tested under a four-point loading system. The tested slabs were divided into two groups according to preloading level to study the effect of cracking level. Two preloadings were selected, i.e. 60% and 80% from the ultimate load. The strengthening techniques used were ferrocement layer, steel plate, carbon fibre reinforced polymers (CFRP) sheets and CFRP strips. The slabs were loaded up to failure and the structural response of each slab specimen was predicted in terms of the onset of cracking, deflection, collapse load and failure mode. The efficiency of different repair and strengthening techniques and their effects on the structural behaviour of cracked concrete slab had been analysed. It was observed that the type of strengthening technique used affect the load carrying capacity, deflection, stiffness and toughness of the slab. All repair techniques were found to be able to restore and enhance the structural capacity of cracked concrete slabs. The enhancement ratio is found to be affected by the preloading or the cracking level.

RECYCLING OF WASTE GLASS IN MORTAR MIXTURES

There is a growing environmental concern in many countries around the world from the accumulation of solid waste glass since not all glass can be recycled into new glass. This study explores the recycling of solid waste glass in concrete mixtures to reduce the environmental pollution and to improve the properties of concrete material. Three waste glass powder (WGP) levels were considered in this study: 5%, 10% and 15%. The properties investigated include: setting time, workability, compressive and flexural strength and micro-structure of mortar. The mortar mixtures proportions were 1:3:0.7 by weight for cement, sand and water, respectively. The results showed that the solid waste glass can be recycled in cement concrete mixtures and improve the properties of concrete. The setting time of cement paste increased and the workability decreased with the increase of the WGP content. The compressive strength of mortar increased with the increase of WGP as partial replacement of limestone sand under moist curing. The flexural strength of mortar increased with the increase of WGP as partial replacement of cement or sand under moist curing. The autoclaved WGP mortar showed higher compressive strength and lower flexural strength compared to the moist cured mortar. The scanning electron microscopy images showed that WGP material is good filler because it reduced the porosity of mortar.

Performance of Olive Waste Ash Concrete Exposed to Thermal Cycling

This paper explores the influence of olive waste ash (OWA) on the performance of concrete to thermal cycling. The performance of concrete to thermal cycling was evaluated by measuring the compressive strength, electrical conductance, and visual inspection of cracks in concrete specimens. Three OWA replacements were utilized in the study: 7, 15, and 22 % by weight of sand. The other experimental parameters investigated in the study were aggregate type (crushed limestone and volcanic pumice), water to cement (w/c) ratio (0.4 and 0.6), and curing type (moist and autoclaving curing). After the initial moist curing, concrete specimens were exposed to thermal cycling regime in the range from 30 to 150°C during a period of 24 h using an electric furnace. The results of the study showed that thermal cycling of OWA concrete resulted in significant cracks and damage in concrete specimens. The OWA concrete was found more resistant to thermal cycling compared to plain concrete. Additionally, the resistance of OWA concrete to thermal cycling increased with increasing the OWA content. The OWA concrete containing pumice aggregate showed more resistance to thermal cycling than OWA concrete containing limestone aggregate. The resistance of OWA concrete at w/c ratio of 0.4 to thermal cycling was observed higher compared to OWA concrete at w/c ratio of 0.6. The autoclaved OWA concrete showed higher improvement to thermal cycling than the moist cured OWA concrete.