Failure mechanism of prepacked concrete

Concrete is a multiphase material in which aggregate particles are distributed in the mortar matrix. Since a large volume of the concrete is occupied by aggregate, it is likely that variation in aggregate content will significantly influence the strength and deformation behavior. Prepacked concrete, as it contains a higher proportion of coarse aggregate, shows characteristics in failure that are widely dissimilar from those of normal concrete. This paper presents some aspects of failure mechanism of prepacked concrete observed during testing in compression. Along with the observations, some theoretical considerations are also made and discussed

Creep recovery of prepacked aggregate concrete

Previously the writer presented the results of a study on the creep and shrinkage behavior of prepacked aggregate concrete. In the same study strain on removal of sustained load was also measured. In this article, results on creep recovery of normal and prepacked aggregate concrete are presented and discussed. It has been observed that the creep recovery of prepacked aggregate concrete is lower than that of normal concret

Creep recovery of prepacked aggregate concrete

Previously the writer presented the results of a study on the creep and shrinkage behavior of prepacked aggregate concrete. In the same study strain on removal of sustained load was also measured. In this article, results on creep recovery of normal and prepacked aggregate concrete are presented and discussed. It has been observed that the creep recovery of prepacked aggregate concrete is lower than that of normal concret

Deformation behaviour of self-compacting concrete containing high volume palm oil fuel ash

Self-compacting concrete (SCC) is an advanced type of concrete that can be placed and compacted under its own mass without vibration. Although SCC can be proportioned with a wide range of constituent materials, the utilization of supplementary cementitious materials can significantly influence the cost and performance of SCC. One of the potential supplementary cementitious materials from palm oil industry is palm oil fuel ash (POFA). The objective of the research project was to evaluate the effects of high volume POFA on the deformation behaviour of SCC. This study outlines laboratory tests, which were conducted through replacing ordinary Portland cement (OPC) by 0%, 50% and 70% of POFA by weight, with water-binder ratio of 0.4. Target properties for SCC workability were studied as a function of the application and in terms of filling ability, passing ability, segregation resistance which include slump flow, J-ring, and V-funnel at T5minutes for fresh properties, and compressive strength, split tensile strength, flexural strength, modulus of elasticity, creep, and shrinkage tests for hardened concrete. Test specimens comprising of cube, cylinder and prism were prepared and tested at 7, 28, 56, and 90 days. Results obtained in this study reveal that high volume palm oil fuel ash used in self-compacting concrete exhibited satisfactory performance particularly at later ages

The effectiveness of palm oil fuel ash in preventing expansion due to alkali-silica reaction

Laboratory tests were conducted to evaluate the performance of palm oil fuel ash (POFA), a recently identified pozzolanic material, in reducing the e.xpansion of mortar bars containing Tuff as a reactive aggregate where ordinary Portland cement (OPC) was replaced, mass for mass, by 0, 10, 30 and 50% POFA. The South Ajiican NBRI Accelerated Test method was used in the experimental investigation, which revealed that palm oil fuel ash has a good potential in suppressing expansion due to alkali-silica reaction

An efficient plasmonic photovoltaic structure using silicon strip-loaded geometry

We show that a silicon thin-film photovoltaic structure with silicon strips on the top and grooves on the silver back contact layer can absorb incident solar energy over a broad spectral range. The silicon strips on the top scatter the incident light and significantly help couple to the photonic modes in the smaller wavelength range. The grooves on the silver back contact layer both scatter the incident light and help couple to the photonic modes and resonant surface plasmon polaritons. We find an increase of ∼46% in total integrated solar absorption in the proposed strip-loaded structure compared to that in a planar thin film structure of same dimensions. The proposed structure offers simpler fabrication compared to similar plasmonic-inspired designs

Influence of palm oil fuel ash on fresh and mechanical properties of selfcompacting concrete

This paper presents experimental results of some fresh and hardened state properties of selfcompacting concrete (SCC) incorporating palm oil fuel ash (POFA). Three concrete mixes namely ordinary Portland cement (OPC) concrete i.e. concrete with 100% OPC as control, and concrete with 30% and 60% POFA having different water/binder (w/b) ratios of 0.4, 0.45 and 0.5 were prepared. Filling ability, passing ability and segregation resistance of SCC along with strength properties were determined and compared with those of the OPC based SCC. Test results revealed that replacement of POFA in general decreased the workability of concrete with acceptable range. The compressive strength, however, increased with lower w/b ratio and lower replacement of ash. The splitting tensile and flexural strength values have also followed the same trend. The results obtained and the observation made in this study suggest that POFA can suitably be used as supplementary cementing material in SCC

Influence of palm oil fuel ash on physico-mechanical properties of prepacked aggregate concrete

Prepacked aggregate concrete (PAC) is a special type of concrete which is made by placing coarse aggregate in a formwork and injecting a grout either by pump or under gravity force to fill the voids. Utilization of pozzolanic materials in traditional concrete has become increasingly extensive, and this trend is expected to continue in prepacked concrete as well. Palm oil fuel ash (POFA) is one of the pozzolanic ashes, which has been recognized as a good pozzolanic material. This paper presents the results of some experimental tests on the performance behavior of POFA in developing physical and mechanical properties of prepacked aggregate concrete. Four concrete mixes namely prepacked concrete with 100% OPC as control, and PAC with 10%, 20% and 30% POFA were cast, and the temperature growth due to heat of hydration in all the mixtures was recorded. It has been found that POFA significantly reduced the temperature rise in prepacked concrete. The compressive and tensile strength, however, increased with replacement of POFA. The results obtained and the observation made in this study suggest that the replacement of OPC by POFA is beneficial, particularly for prepacked mass concrete where thermal cracking due to extreme heat rise is of great concern