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Used engine oil (UEO) is recognized as a hazardous waste produced during engine servicing. Its disposal in an environmentally friendly manner is a big challenge. This paper presents the experimental results of an investigation of the effects of UEO on slump and hardened concrete properties. Three concrete groups; 100% cement (OPC) concrete, concrete with 60% OPC + 40% fly ash and concrete with 80% OPC + 20% rice husk ash were prepared. Each of the groups composed of a control mix and a mix with 0.15% dosage of UEO (this dosage was selected from previous studies). Slump measurement of fresh concrete confirmed that a small dosage of UEO reasonably improves the slump of concrete. Lignosulfonate molecule (a common class of water reducing admixture) consists of aromatic rings containing one of the ionic groups viz., OH−, COO−, SO32−. The chemical composition of used engine oil showed the presence of 37% SO3 content that may be the reason for the plasticizing effect. Used engine oil caused variation in the compressive strength in the range of ±20% as compared to the control mix. The compressive strength at 28, 56, and 180 days of 100% OPC concrete with UEO reduced by about 17%. In general, a small dosage of used engine oil caused a substantial reduction in coefficient of oxygen permeability and porosity of all concrete mixes, which is an indicator of enhanced long-term durability.

This paper presents the effects of the specially designed solarcure method on the properties of geopolymer binders. The solarcure method is composed of the box-shaped chamber that works on the principles of trapping solar radiations to regulate the adequate amount of heat and temperature inside the box. Two sets of geopolymer binder mix containing low-calcium fly ash (LCFA) and high-calcium fly ash (HCFA) as a base material was developed. One part of sodium hydroxide (5 M and 10 M) solution mixed with two parts of sodium silicate was used as an alkaline activator. Mortar cubes of 50 mm size were cast and cured in three different regimes; continuous oven (CO) curing, intermittent oven (IO) curing and solarcure (SC) curing were used for the compressive strength test. For constant curing; temperature was maintained at 60 °C 24-h, whereas in intermittent conditions (IO and SC), samples were cured in three cycles; each cycle was composed of 8 h curing then 16 h cooling. For IO curing, the oven temperature was maintained at 60 °C, however for SC curing; the solar-box chamber has achieved maximum inside temperature up to 90 °C for each curing cycle. Specially designed SC technique caused up-to 56% increase in compressive strength as compared to the compressive strength of CO cured samples. SC curing also improved the microstructure properties and geopolymer reaction product.

Externally strengthened marine concrete structures by using carbon fiber-reinforced polymer (CFRP) are being used more extensively because of their exceptional properties, including high corrosion/environmental degradation resistance. Debonding of CFRP sheet from the concrete substrate is one of the typical failure modes observed by using this technique. Therefore, the strengthening technique efficiency strongly depends on the effectiveness of the CFRP-concrete bond. Numerous experimental studies have been conducted to investigate the bond behavior and most of the proposed bond strength models considering the influence of the effective bond length. This study was conducted to experimentally investigate the effective bond length of CFRP sheets subjected to marine environment exposure, which is identified as one the major gaps in this discipline. The concrete beam specimens exposed to marine environment were tested to determine the effective bond length. The three-point bending-type shear bond test was used to obtain the stress versus load relationship. The test variables were the type and exposure duration. The test results showed that the marine environmental exposure significantly influenced bond stress and effective bond length. Two factors, CFRP stiffness and concrete compressive strength, contributed to fix the effective bond length of the CFRP-concrete interface. The maximum bond stress, after 12 months of wet/dry cyclic exposure, was found higher than that subjected to full immersion exposure. The average maximum bond stress decreased with an increase in full-immersion exposure time to 12 months. Results indicated that the exposure condition influences the capacity of CFRP-concrete bond and resulted in a reduction in effective bond length by 16–29%. Moreover, debonding was observed as the dominating mode of failure for all tested specimens. The prediction models of effective bond length, considering the influence of marine environment, are also established. Therefore, the outcome of this study will help to resolve one of the debonding issues in strengthening marine structures.

This paper presents an experimental study on improving the post-cracking and the fracture behavior of engineered geopolymer composite containing polyvinyl alcohol (PVA) fibers. Two classes of fibers designated as coarse and fine were investigated. The single fiber volume governed the total number of fibers dispersed in the unit volume of the matrix (Nv), which caused significant effects on the post-cracking and the fracture behavior of the composite. The molarity of the NaOH solution is an important parameter that controlled the geopolymerization process and affected the strength and other properties of the composite. Three different molarity of NaOH solution, 8 M, 12 M, and 16 M, were investigated. The results showed that the specimens made of 8 M matrix containing fine fibers (0.04 mm diameter and 8 mm and 12 mm in length) performed well in the post-cracking stage and satisfied the criteria for pseudo strain hardening (PSH). The direct tensile strength results showed that 8 mm and 12 mm long fine fibers in the 8 M matrix achieved the strength ratio of ultimate to the first crack strength as 1.7 and 1.66, respectively. The strength ratio criterion for PSH suggested a value greater than 1.3. Similarly, from the notched-beam bending test, the energy performance index of 8 mm, and 12 mm long fine fibers in the 8 M matrix were estimated as 7.77 and 6.52, respectively. In contrast, a value of greater than 3 is recommended for PSH behavior. Fine fibers added in the 12 M and 16 M matrix also satisfied the criteria for PSH behavior. Whereas, the coarse fibers (0.2 mm diameter and 18 mm and 24 mm in length) performed well in resisting direct compression and showed higher fracture energy and the modulus of elasticity. The best combination was observed as a 12 M matrix containing fine fibers of 0.04 mm diameter and 8 mm in length.

This experimental investigation has been carried out to examine the effects of temperature and duration on Malaysian kaolin to form highly reactive metakaolin. Metakaolin has been produced through the calcination process at temperatures 600–800 °C (1112–1472 °F) for the duration from 1 to 5 h. X-ray diffraction and loss on ignition are the usual process to identify the optimum temperature and duration of calcination required. In this study, to confirm the reactivity of metakaolin, compressive strength, splitting tensile and flexural strength of concrete at the age of 7, 28, 56 and 90 days have been investigated using locally produced metakaolin as cement replacing material. It was found that locally produced metakaolin enhance the mechanical properties of concrete and compressive strength is about 5% higher than silica fume concrete at the age of 28 days. This study divulges that calcination at 800 °C (1472 °F) for 3 h is the most suitable condition to convert kaolin into highly reactive metakaolin.

This paper presents an experimental study of the influence of different superplasticizer dosage on compressive strength and micro-structure characteristics of interfacial transition zone (ITZ) prepared with fly ash based self-compacting geopolymer concrete (SCGC). The correlations between compressive strength development and microstructure of interfacial transition zone were also investigated. Concrete specimens were prepared with different superplasticizer (SP) dosage namely 3%, 4%, 5%, 6% and, 7% and cured at 70 °C for duration of 48 h. Field emission scanning electron microscope (FESEM) observations revealed that improved performance of concrete was found when the compressive strength increased through formation of dense ITZ between the aggregate and binder matrix at higher SP dosage. There are good correlations between compressive strength and micro-structure characteristics of interfacial transition zone. The FESEM analysis revealed that relatively a loose and porous interfacial zone was found between the binder and aggregate for low SP dosage and theses loose and porous ITZ decreased the performance of concrete by lowering the compressive strength; however, a dense ITZ was found between the aggregate and binder matrix for higher SP dosage that enhanced the concrete performance by increasing the compressive strength.

The development of fly ash and microwave incinerated rice husk ash (MIRHA) blend as the source material for geopolymer concrete was studied through the observation of the hardened specimen strength. Compressive and bonding strength of the specimen indicate the significance of curing temperature in the activation of MIRHA particles. The elevated temperature is presenting a suitable condition for rapid dissolution of silicate monomer and oligomer from MIRHA surfaces, which supports the formation of supersaturated aluminosilicate solution in geopolymer system. It contributes to the refinement of pores structure via the increasing geopolymer gel growth, as observed in the consistent compressive strength development of ambient-cured specimen to the oven-cured specimen. Densification of geopolymer framework appears to be the main contributor to the increasing bonding capacity of geopolymer binder. 2012 Elsevier Ltd. All rights reserved.