M. S. Hamidah

Microorganism Precipitation in Enhancing Concrete Properties

Microorganism is an unique living element and has the ability to precipitate minerals through the process of biomineralisation. The precipitation process occured naturally and most of the precipitated products are very important compound composed of such as carbon, nitrogen, oxygen, sulphur, phosphorus and silica. So far, concrete incorporated with microorganism that able to precipitate calcium carbonate (calcite) was reported. However, little information on silica precipitation and its effect on concrete properties has been revealed. In this present study, the concrete specimens were incorporated with Bacillus subtilis silica adsorbed in their cell wall. Concrete specimens with five different concentration of Bacillus subtilis cell which are 104, 105, 106 and 107 cell/ml and control (without Bacillus subtilis) were cast. The experimental investigation aims to prove that the silica precipitated by this microorganism can enhance the concrete properties namely its compressive strength and resistance to carbonation. The microstructure of the concrete contained Bacillus subtilis was also examined. It appears that the inclusion of Bacillus subtilis into the concrete enhanced the compressive strength. The concentration of 106 cell/ml was found to be the optimum concentration to give most enhanced effect to the compressive strength. However the effect of including Bacillus subtilis to the resistance to carbonation of the concrete specimen is found to be insignificant.

Chloride Permeability of Nanoclayed Ultra-High Performance Concrete

It is widely recognized that the ingress of chlorides into concrete can initiate reinforcement corrosion and ultimately result in deterioration of the concrete structure. Chloride permeability of concrete has been recognized as a critical intrinsic property affecting the durability of reinforced concrete. From the previous research, the use of nano clay (NC) in cement mortar due to chloride permeability has been well-documented. In this paper, the ability of ultra-high performance concrete (UHPC) to withstand the action of chloride penetration were investigated. An experimental research was carried out in order to investigate the influence of incorporating NC material as cement replacement into ultra-high performance concrete (UHPC-NC) on chloride-related transport characteristic. The workability, compressive strength and charge passed in rapid chloride permeability test (RCPT) of UHPC-NC were reported. Those parameters were also determined for normal strength concrete (NPC) and plain without nano clay ultra-high performance concrete (UHPC) as comparison. Three (3) series of UHPC-NC mixes were produced incorporating 1 % (UHPC-NC1), 3 % (UHPC-NC3) and 5 % (UHPC-NC5) of NC replacing cement (OPC). The results showed that incorporating NC in concrete mixes causes a reduction in the workability. It was also found that replacing of OPC with NC improved the strength of UHPC-NC as compared to those mixes without NC material. The optimum NC replacement level recorded at 3 % (UHPC-NC3) from the total weight of OPC. For the chloride permeability, it is clearly shown that the presence of NC has important benefit in terms of chloride resistance.

Alteration of Nano Metakaolin for Ultra High Performance Concrete

The utilization of Ultra High Performance Concrete (UHPC) in the construction industry is growing towards in the new millennium. UHPC produce a very high strength and durable concrete to withstand aggressive attack from nature such as sulphate, chloride and others. The production of UHPC depends on several factors for instance high consumption of cement, very fine aggregates, utilizing pozzolanic material such as silica fume and additions of hyper plasticizers. Now days with the recent development of nanotechnology, nano materials has been produced and utilize in the concrete. Due to the effects of ultrafine particles, nano material will helps to enhance strength and durability of conventional UHPC mix. In this research, nano metakaolin has been developed by using high energy milling from raw kaolin. Zirconia oxide of jar and ball were used and the duration of milling is 24 h. The mix proportion of this research also includes metakaolin as cement replacement material to 10 % and nano metakaolin as additives from 1, 3, 5, 7 and 9 %. Nano metakaolin inclusion in UHPC mix will be evaluated for cementitious properties in terms of standard consistency and setting time whereas for mechanical properties compressive strength test will be performed. For setting time shows that the addition of nano metakaolin at every replacement level will increase setting of cement paste and the optimum retardation effect were recorded by NKA1. The addition of nano metakaolin at 7 % records the highest strength compare to other specimens. The action of nano metakaolin at 1 % acts as ultra-filler and refines the microstructure of concrete. Furthermore, nano metakaolin also produces a secondary hydration product by optimizing the remaining calcium hydroxide which was not fully removed during the hydration period.

Fatigue Crack Inspection and Acoustic Emission Characteristics of Precast RC Beam under Repetition Loading

Fatigue crack of the precast reinforced concrete beam under repetition loading is vital to be examined. Reinforced concrete structures exposed to excessive repetition loading could lead to the failure of the structures. In order to examine the active fatigue crack, the reinforced concrete beams were subjected to three-point repetition maximum loading. Eight phases of maximum fatigue loading with sinusoidal wave, frequency of 1 Hz and 5000 cycles for each phase were performed on the reinforced concrete beams. The inspection was carried out with visual observation of the crack pattern and acoustic emission technique for each load phase. The signal strength of acoustic emission was investigated. It is found that the signal strength of acoustic emission and crack pattern of the reinforced concrete beam subjected to repetition loadings showed promising results for structural health monitoring.

Bonding Strength of Expanded Polystyrene (EPS) Beads Enhanced with Steel Fiber in Reinforced Lightweight Concrete (LWC)

Lightweight concrete (LWC) is one of the favourable concrete to be used as it has low density with acceptable high strength, high durability, and toughness. In order to produce LWC, it is required special material such as expanded polystyrene (EPS) beads and steel fiber to be added into the design mix concrete. As known, EPS beads have zero strength. Meanwhile, the significant of steel fiber is to reduce micro and macro crack propagation. Therefore, pull out test were carried out to measure the bond strength between reinforcement bar and three series of concrete mix design which are normal concrete, EPS-LWC and EPS-LWC enhanced with steel fiber. Concrete adhesion and bearing deformation of reinforcing bar against the concrete are the two main mechanisms that influence the strength of bond in the steel reinforced concrete. Deformation will increase when the bonding stress increase. Normal concrete series shows the higher average bonding stress which is 531.22 kPa compared to others series concrete mix. Meanwhile, bonding stress of EPS-LWC mix is 174.54 kPa which is higher than EPS-LWC enhanced with steel fiber mix. Even though the present of the steel fibre can increase the strength of the LWC, but it effects to the bonding strength between reinforcement steel rod and concrete. There are two improtant factor in bonding determination which are volume fraction and aspect ratio of the steel fiber. Segregation will increase when the aspect ratio of steel fiber increased. Besides, the workability becomes low. This present study used types of hooked end steel fiber with 60 mm length and aspected ratio is 0.75. While the size of the cylindrical is 300 mm x 150 mm. The position of the steel fiber in the specimens is too compact and presenting the air voids. Consequently weaken the bonding strength between concrete and reinforcement bar.

Effect of Clay as a Nanomaterial on Corrosion Potential of Steel Reinforcement Embedded in Ultra-High Performance Concrete

The effect of clay as nanomaterial or nanoclay (NC) on corrosion potential of steel reinforcement embedded in ultra-high performance concrete (UHPC) due to the early age properties of UHPC was investigated. In this present research, ordinary Portland cement (OPC) was partially replaced by NC at 1, 3, and 5 % by weight of cement to produce the nanoclayed UHPC. It is well recognized that the corrosion of steel reinforcement would affect the service life of the reinforced concrete structure performance. To overcome this problem, UHPC was benefited due to its superior characteristic in term of density and durability as compared to OPC concrete itself. In this present research, half-cell potential (HCP) was used to monitor and measure the corrosion potential of steel reinforcement embedded in UHPC and nanoclayed UHPC. Meanwhile, weight loss of corroded steel reinforcement and pH values of hardened UHPC and nanoclayed UHPC were also conducted as follows to the specific procedures. All the samples were immersed in 3 % sodium chloride solution up to 91 days of exposure. The results revealed that the corrosion activity of steel reinforcement embedded in UHPC with 5 % NC recorded the lowest corrosion potential readings compare to those UHPC. It is also shows that the pH value of concrete and weight loss of corroded steel reinforcement in UHPC alone is highest compared to UHPC incorporating different levels of NC. As regards to the results, it is revealed that replacing NC as a replacement to cement significantly enhanced the chloride penetration of nanoclayed UHPC. It is also indicated that the corrosion potential decreased with the increase of NC and as a result delayed the corrosion initiation.

Effect of Heat Treatment on Mechanical Properties of Ternary Blended Eco-friendly UHPFRCC

The rapid expansions in economic development, urbanisation and above all population have been accompanied by an upsurge in the accidental fire hazard. The fire redundancy of buildings can decrease the risk of damage and injury by improving the safety of residents and also by enhancing the reusability of buildings. In the recent decades, investigations on elevated temperature resistant passive fire protection layers have been progressing with the use of several environmental friendly materials. However, there is an inadequate information on the effect of heat treatment on the ultra-high performance fibre-reinforced cementitious composites (UHPFRCC) containing high-alumina cement (HAC), ground granulated blast furnace slag (GGBS) and fly ash (FA) in conjunction with hybrid fibres (basalt and polypropylene fibres), which could be a potential fire resisting UHPFRCC for the structural members. The effect of heat treatment on the compressive strength and flexural strength of UHPFRCC, made of ternary blend and hybrid fibres, was investigated in this study. Besides control sample, five other UHPFRCC samples were prepared. After 28 and 56 days of normal curing, each of the samples was held at room temperature as well as exposed to 400, 700 and 1000 °C, then tested. Examination of results disclosed that the UHPFRCC with the replacement of 25 % of fly ash with GGBS, in conjunction with hybrid fibres, possessed highest residual compressive strength in the temperature range of 28–900 °C with 48 % of RCS value at 900 °C after 56 days of curing. However, in the range of 28–1000 °C, UHPFRCC with PP fibre and hybrid fibre performed almost equally well with the residual flexural strength value of 36 % at 1000 °C after 28 days of curing.

Autogenous Healing Mortar Made of Alginate-Encapsulated Geobacillus Stearothermophilus

The autogenous healing by microbial induced calcite precipitation (MICP) has become significant interest in sustainable approaches on concrete repair and maintenance. Alginate-encapsulated Geobacillus stearothermophilus is introduced as a new smart material for self-healing concrete. Its effects on concrete performance were evaluated with regard to strength enhancement and healing efficiency. The aim of this study was to optimize bacteria cell concentration and alginate-encapsulated Geobacillus stearothermophilus (AE-GS) composition in the concrete mixture in order to obtain the maximum healing capacity by using response surface methodology approach. Verification tests have shown the successful relation developed by statistical treatments; due to the potential of Geobacillus stearothermophilus immobilized into sodium alginate gels that can act as a guideline in the mixture proportion of autogenous healing concrete in a future.

Characteristic and Strength Properties of Nano Metaclayed UHPC

Nanometal clay formerly known as nanoclay was a product from kaolin. Nanoclay considered as layered silicate mineral and potentially can be used as supplementary material in concrete study due to kaolinite compound in its chemical composition which is similar to metakaolin. In this study, formulation of nano metaclay where used as additives from 0, 1, 3, 5, 7, and 9 % in ultra-high performance concrete mix. This paper aims to study the effect of nano metaclay in morphology which includes XRF, SEM, and XRD analysis, characteristics of nano metaclay UHPC mix in workability, and also to see the hardened properties by means of compressive strength behavior and micrograph image of UHPC. All nano metaclayed UHPC mix will be compared to normal UHPC mix. As a conclusion, nano metaclay ball-forming structure provides a new knowledge on nano materials in concrete. Due to its clay properties, water demand is higher and decrease in fresh state occurred. Finally, addition of nano metaclay UHPC improves compressive strength of UHPC mix by acting as nano filler and promoting nucleation process in cement grain.

Strength development of fine grained mortar containing fly ash and rice husk ash

Fine grained mortar (FGM) offers a new innovative technology binder system. The innovative technique is achieved by using a small maximum grain size of 600μm for the mortars. Most of the previous studies have focused on the FA to be replaced in the FGM. There is still lacking of research of using other pozzolanas in making FGM. This paper presents a study of the strength of FGM with partially replacement of ordinary Portland cement (OPC) with fine fly ash (FA) and ground rice husk ash (RHA). Flexural and compressive strength of FGM were tested. The results show that the use of FA and RHA produces FGM with improved strength with the replacement up to 20% than that of the control FGM. The use of FA and RHA is very effective in enhancing strength at the later age of FGM.