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Heat cycling of epoxy mortar repaired beams
Abstract
The use of epoxy patch repair materials has gained in popularity in both temperate and hot climates over the past two decades. Temperatures in hot climates can vary significantly over a 24 hour period. In the Gulf Region daytime temperatures in the shade can commonly exceed 50 C (122 F), with the night temperatures dropping to single figures. In such climates the sun usually shines for long periods, raising temperatures of surfaces in direct sunlight to even higher values. To investigate the above, five reinforced concrete beams with a preformed fault, repaired with Lightweight Epoxy Render (LWER), were subjected to 1000 heat cycles prior to being tested statically. Pull-off bond tests were then carried out on these beams to investigate the effect of heat cycling on the bond strength between the LWER and concrete substrate. The heat cycling of the epoxy repaired beam showed that the bond between the repair material and the concrete substrate remained intact. The cycling, however, did cause the epoxy render to crack. These cracks were similar to shrinkage cracks and extended into the beam section to the shear reinforcement.
... In this investigation, three types of materials were used representing the full range of repair materials available, namely, a basic cementitious, a polymer modified cementitious and an epoxy render. The main properties of the three materials including bond strengths were reported by Abu -Tair et al [4][5][6][7][8], Abu -Tair el al [9] also reported on the effectiveness of resin injection of cracked reinforced concrete beams similar to those in this investigation and using similar loading systems. The cost of the repair materials is a major factor in deciding on a repair system, the cost of typical cementitious: polymer modified: epoxy mortars vary in the ratio 1:6.5:20 respectively [10]. ...
... In this investigation, three types of materials were used representing 7 the full range of repair materials available, namely, a basic cementitious, a polymer-modified 8 cementitious and an epoxy render. The main properties of the three materials including bond 9 strengths were reported by Abu -Tair et al [2][3][4][5][6], Abu-Tair el al [7] also reported on the 10 effectiveness of resin injection of cracked reinforced concrete beams similar to those in this 11 investigation and using similar loading systems. The cost of the repair materials is a major 12 factor in deciding on a repair system, the cost of typical cementitious: polymer-modified: 13 epoxy mortars vary in the ratio 1:6.5:20 respectively [8]. 14 ...
The repair and strengthening of concrete structures has become a significant area of specialization in the construction industry, in many countries the cost of repair and strengthening is accounting for nearly 50% of the overall expenditure within the construction industry. Generally, concrete properly made and compacted has a high resistance against deterioration and possible damage. However, structures may suffer damage or deterioration from a variety of internal and external causes. Repair may be carried out to protect the reinforcement, to restore the structure to its original strength, or merely to restore the original appearance. Whatever the reason, an essential requirement is that the repair achieves a satisfactory bond with the substrate concrete and maintains good adhesion and protection over the service life of the structure. A range of repair materials and techniques are available to the maintenance engineer, the selection of the best suitable materials and most effective technique are essential in a durable and effective technique. In this investigation, three types of materials used to represent the full range of repair materials available, namely, a basic cementitious, a polymer-modified cementitious and an epoxy render. Twelve reinforced concrete beams, with preformed faults, were repaired and tested under three loading systems, a static loading, a service level cyclic loading and a near ultimate fatigue loading, the results from these beams were compared to control beams with similar reinforcement and made from similar concrete, but with no faults.
... In the desert areas of the middle east the temperature during the day reaches 50°C in the shade and direct solar radiation increases the temperature of exposed concrete surfaces by 15-20°C (Abu-Tair et al., [1], El-Menshawy, [2]). At night there is a sharp drop in temperature. ...
In this investigation, the effect of simulated desert climate on moisture loss (as it is related to drying shrinkage), ultrasonic pulse velocity (internal crack detector), absorption (durability index) and compressive strength (mechanical properties pointer) were studied. Concrete mixes, having w/c ratios of 0.35, 0.45 and 0.55 and polypropylene fiber volumes of 0, 0.1, 0.2 and 0.3%, were prepared and subjected to one of three conditioning regimes after 14 days of moist curing. The samples were either kept in laboratory air, placed in an oven operating two daily temperature cycles between 75 °C and room temperature or placed in a continuous heating oven at the same temperature. It was found that heating adversely affected all studied properties of concrete. The moisture loss and absorption were increased by a factor that ranged between 4.23-29.96 or 2.8-18.67, respectively. The compressive strength was reduced by 3.16 to 33.82% compared to the samples kept in laboratory air. The inclusion of fibers improved the performance of concrete mixes compared to the no fiber mixes subject to temperature, to a certain degree. Fiber volumes 0.1-0.2% are recommended in these conditions depending on the type of mix. The presence of polypropylene fibers interferes with the elastic waves traveling through concrete and hence reduces the pulse velocity. Heating of fiber concrete seems to magnify this interference and therefore ultrasonic pulse velocity readings could not be used as internal crack indicators in the current study. ت ا رة ارة ٤٢٣-٢٩٩٦ ا هاء ا ات ا ا أﻡل. ار ص اﻡ زاد أ و ٢٨-١٨٦٧ ا ا ت ص اﻡ ل أﻡ. ﻡوﻡ أﻡ ا ارة ا ات ا ٣١٦-٣٣٨٢ % ا ا ت ﻡر ا هاء. و ا أف اام أن و ٠١-٠٢ % ﻡ ا اهر ارة اض ﻡ. ا و ا أف ود أن ا ها و ارة ض داد ا ها و ا ق ات. ا ق ات ا ها اارة ﻡ ا ااﺥ خ ﻡا ﻡ. INTRODUCTION In the desert areas of the middle east the temperature during the day reaches 50°C in the shade and direct solar radiation increases the temperature of exposed concrete surfaces by 15-20°C (Abu-Tair et al., [1], El-Menshawy, [2]). At night there is a sharp drop in temperature. It has been shown that this cyclic change in temperature causes severe microcracking due to thermal incompatibility of concrete components, which in turn leads to an increase in the concrete permeability and a reduction in its tensile strength (Rasheeduzzafar and Al-Kurdi, [3]). The effect of the heat cycles (80 °C for 24 hours followed by room temperature for 24 hours) on some mechanical properties of concrete has been studied by Al-Tayyib et al. [4] who found that the compressive and flexural strengths were reduced by 27 and 32%, respectively. Rasheeduzzafar and Al-Kurdi [3] reported that the w/c = 0.4 concrete was less damaged by daily heat cycles (27 to 60 °C) compared to the w/c = 0.6 concrete.
... The performance of the RMs in service under structural loading has received relatively little attention from the research community, especially in the case of patch repairs. Some studies have considered the behavior of repaired reinforced concrete members under service loads (Abu-Tair 1997;AlFarabi et al. 2006;Ghassan and Zai-UL-Hasan 1999;Rio et al. 2005). However, there is no agreement between researches regarding the properties, which should be considered in the evaluation. ...
Structural elements such as beams, slabs, and columns may require strengthening or repair during their service life. Different repair materials (RMs) are available and it is usually difficult to choose the best ones, especially when considering the cost of such materials. This paper presents the results of an experimental investigation of patch RMs on plain concrete prisms as well as on reinforced concrete beams. Three cement-based RMs available in the market with different mechanical properties and an ordinary Portland cement (OPC) mix produced in the lab were used in the study. Damage was induced in prisms/beams and then repaired using different materials. The experimental work included assessment of the flexural strength of damaged/repaired plain concrete prisms; slant shear (bond) strength between the concrete and the RM; axial strength of damaged/repaired plain concrete prisms and bond of the repair materials in damaged/repaired reinforced concrete beams loaded to failure. The test results showed that all RMs performed well in restoring the strength of damaged plain concrete. Compatibility of the RMs with substrate concrete was found to be more important in the behavior than superior mechanical properties of the RMs. No difference was noted in the behavior between the RMs in repairing reinforced concrete beams at the tension side.
The paper examines the properties of five different types of repair materials, including conventional cementitious, polymer and polymer-modified repair mortars. Assessment was carried out on the basis of the engineering properties (compressive strength, tensile strength and modulus of elasticity), pore structure (porosity and pore size distribution), transport properties (permeability and diffusion) and shrinkage. These properties were measured up to the age of 28 days after curing in a hot-dry environment.The epoxy resin repair mortar showed superior strength and transport characteristics with a very fine pore structure; however, its modulus of elasticity was remarkably low when compared with that of normal- and high-strength concretes. A hot-dry curing environment adversely affects the shrinkage and performance-related properties of conventional repair mortars; however, small improvements could be achieved by the use of mineral admixtures (fly ash and silica fume). The paper discusses also the different testing techniques which could be used to assess the potential performance of concrete repair mortars.
The effectiveness of the method of resin injection in restoring the structural integrity of crack-damaged reinforced concrete beams was investigated. Fourteen beams that had been tested previously under static loading in a study into the performance of patch repair materials were resin injected. The beams were evaluated under three load systems, one static and two cyclic. Three of the beams were submerged in water at 38°C for 4 months before being tested. Twenty-five cores were taken from the beams to study injected cracks under a microscope. The load tests have shown that the resin injection successfully restored the beams to their original strength and stiffnesses. The prolonged load cycling under very high stress levels, and the soaking in water at 38°C for 4 months, did not cause the cracks to reopen. Microscopic examination has confirmed the effectiveness of the resin systems in penetrating even the very fine ends of the cracks.
The effect of hot-humid climate on compressive strength of mortar was investigated. The variables studied were air and mortar temperatures and type of cement. The results show that prolonged exposure to hot-humid climate affects adversely the later age strengths. However, there is an indication that mortar or concrete exposed to hot-humid climate for its life might attain a strength equal to (or even higher than) that received at normal conditions.