Bond Strength of Fusion Bonded Epoxy-Coated Reinforcement in Concrete

Fusion-bonded epoxy-coated steel is expected to extend the service life of the reinforced concrete structure in chloride-laden environments. However, the effect of coating on the bond-strength between rebar and concrete is not well understood yet. This research, therefore, studied the effect of epoxy-coating on the bond characteristics of reinforcing bars in concrete. The bond characteristics were assessed through pullout test considering variables viz. concrete strength, embedded length and bar diameter. The load was applied to reinforcing bars embedded in concrete until bond strength between the bar and concrete exceeded. Bond strength of epoxy-coated bars was compared with that of the uncoated bars. It was found that epoxy-coating reduced the bond strength approximately 25% for Ø20mm bar and 12% for Ø16mm and Ø12mm bar. As with uncoated bar, bond strength of coated bars were also increased with concrete strength. However, the bond strength ratio between coated and uncoated bars was found almost independent of concrete strength. Based on the test results, a development length modification factor of 1.33 is proposed for Ø20mm bar and 1.15 for Ø12mm and Ø16mm bar to compensate the bond strength reduction due to the epoxy coating

Using Jute Fiber to Improve Fresh and Hardened Properties of Concrete

The brittle nature of concrete sometimes makes it challenging for many critical applications. Research has indicated that including discrete short-length, closely spaced fibers in concrete could improve its ductility and act as a crack arrester. As Bangladesh is the prime producer of natural fiber jute, this research aimed to improve the concrete property with this biomaterial. Laboratory work evaluated the mechanical property and shrinkage cracking resistance of jute fiber reinforced concrete with different fiber fractions (viz. 0.1%, 0.2%, 0.3%, and 0.4% by concrete volume) and lengths. The fibers were designated J20 and J25 for 20 and 25-mm lengths, respectively. A portion of the fiber was treated with alkali before using in concrete to improve its property. Jute Fiber Reinforced Concrete (JFRC) was analyzed qualitatively, semi-quantitatively, and quantitatively for compressive, splitting tensile strength, and plastic shrinkage cracking. It was found that the compressive and splitting tensile strengths can be improved by 7% and 25%, respectively. Furthermore, the bio-fiber had a significant influence on shrinkage crack control. In a controlled environment, up to 61% crack area and 62% maximum crack width reduction were achieved. Overall, jute fiber was found to be a sustainable biomaterial for concrete construction in an arid region

Investigating Techniques for Evaluating Fly Ash Behaviour in Air-entrained Concrete

Abstract The paper describes research from a study carried out to investigate techniques for evaluating fly ash influences on air-entrainment in concrete and covers the potential of dye adsorption tests, i.e. using methylene blue (MB) and acid blue 80 (AB80), in this role. The MB test is essentially that given in BS EN 933-9 (normally used for the assessment of fines in sand) and involves visual determination of an endpoint, while the AB80 test (similar to those used for examining activated carbon) is spectroscopic and, therefore, instrument-based. Following the determination of suitable procedures for the tests, their evaluation with fly ashes covering a range of properties is described through comparisons against parameters including, loss-on-ignition and specific surface area (measured by N 2 adsorption). Relationships are presented that examine the dye adsorption of fly ash with respect to the air-entraining admixture demand to achieve a target air content range (5.0 ± 1.0%) in corresponding concretes. These indicate strong correlations for the materials used. Consideration is given to how the dye adsorption tests could be applied in air-entrained fly ash concrete production

Influence of Portland cement characteristics on air-entrainment in fly ash concrete

A study examining air-entrainment in fly ash concretes combined with different Portland cements (PCs) is described. Tests were carried out (using five PCs, ten fly ashes and a standard chemical reagent (to entrain air)) on paste suspensions (foam index), mortar and concrete to quantify the material effects. Preliminary tests indicated that the foam index increased with the fineness (specific surface area (SSA) (by nitrogen adsorption Brunauer–Emmett–Teller (BET) method)) of the PC used (varied by grinding) with fly ash. Reductions in the property were found with increasing alkali content in the paste suspensions (by sodium hydroxide addition), which tended to be slightly greater with higher SSA/lower alkali content fly ash. Tests on the wider range of PCs and fly ashes gave a strong correlation between their combined SSA and foam index, with their combined alkali content having less effect on the latter. The influence of fineness was again apparent in the mortar tests, which also showed that when PC and fly ash were of comparable SSA, a change in either material had a similar effect on air-entrainment. However, fly ash had an increasing influence as the difference in this between materials became greater. The results also suggest that air losses after mixing tend to increase with the SSA of PC + fly ash (and hence admixture dose). Similar effects were generally noted in the tests made on concrete. A possible approach to controlling air-entrainment in fly ash concrete may therefore be to ensure that its SSA is similar to that of the PC with which it is used. A test method to enable this to be evaluated is suggested. </jats:p