Current Issue : January - March Volume : 2015 Issue Number : 1 Articles : 6 Articles
Rice husk ash (RHA) is classified as a highly reactive pozzolan. It has a very high silica content similar to that of silica\nfume (SF). Using less-expensive and locally available RHA as a mineral admixture in concrete brings ample benefits to the costs,\nthe technical properties of concrete as well as to the environment. An experimental study of the effect of RHA blending on\nwork ability, strength and durability of high performance fine-grained concrete (HPFGC) is presented. The results show that the\naddition of RHA to HPFGC improved significantly compressive strength, splitting tensile strength and chloride penetration\nresistance. Interestingly, the ratio of compressive strength to splitting tensile strength of HPFGC was lower than that of ordinary\nconcrete, especially for the concrete made with 20 % RHA. Compressive strength and splitting tensile strength of HPFGC\ncontaining RHA was similar and slightly higher, respectively, than for HPFGC containing SF. Chloride penetration resistance of\nHPFGC containing 10ââ?¬â??15 % RHA was comparable with that of HPFGC containing 10 % SF....
The concept of horizontal shear connection utilization on woodââ?¬â??concrete beams intends to be an alternative connection\ndetail for composite woodââ?¬â??concrete decks. The volume of sawn-wood is over three times more expensive than concrete, in Brazil.\nIn order to be competitive in the Brazilian market we need a composite deck with the least amount of wood and a simple and\ninexpensive connection detail. This research project uses medium to high density tropical hardwoods managed from the Brazilian\nAmazon region and construction steel rods. The beams studied are composed of a bottom layer of staggered wood boards and a top\nlayer of concrete. The wood members are laterally nailed together to form a wide beam, and horizontal rebar connectors are\ninstalled before the concrete layer is applied on top. Two sets of woodââ?¬â??concrete layered beams with horizontal rebar connectors\n(6 and 8) were tested in third-point loading flexural bending. The initial results reveal medium composite efficiency for the beams\ntested. An improvement on the previously conceived connection detail (set with six connectors) for the composite woodââ?¬â??concrete\nstructural floor system was achieved by the set with eight connectors. The new layout of the horizontal rebar connectors added\nhigher composite efficiency for the beams tested. Further analysis with advanced rigorous numerical Finite Element Modeling is\nsuggested to optimize the connection parameters. Composite woodââ?¬â??concrete decks can attend a large demand for pedestrian\nbridges, as well as residential and commercial slabs in the Brazilian Amazon....
This paper presents the findings of an investigation of the fiber content variations in concrete being discharged from a\nready-mix truck at the construction site. Concrete samples were extracted from the truck drums at the beginning, middle and end of\ndischarge. Subsequently, fibers in each sample were separated from the concrete, and weighed. Presumably, synthetic macro fibers\nwill float towards the top, i.e. towards the drum opening, of the inclined, revolving truck-drum, while, on the other hand, steel\nfibers will tend to gravitate towards the lower parts of the mixer drum. Accordingly, the discharge batch, containing synthetic\nmacro fibers, will contain a higher amount of synthetic fibers per unit volume at the start of discharge than the average unit volume\nfiber content of the mix, and the content will gradually decrease further down the batch. The discharge batch of steel fiber concrete\nwill contain fewer fibers per unit volume at the start of discharge than the average unit volume fiber content of the mix, and the\ncontent should gradually increase further down the batch. The correctness of the foregoing is partly confirmed. A certain\npercentage of the truck loads did not comply with the proposed requirements, mainly steel fiber reinforced batches, indicating the\nnecessity of a code or guideline amendment. A change in the Norwegian shotcrete directive was made in 2011, based upon\nexperimental research work (2010), which, in combination with the subsequent University of Life Sciences report (2012),\nconstitutes the foundation of this article....
Alkali-activated slag concretes are being extensively researched because of its potential sustainability-related benefits.\nFor such concretes to be implemented in large scale concrete applications such as infrastructural and building elements, it is\nessential to understand its early and long-term performance characteristics vis-a-vis conventional ordinary portland cement (OPC)\nbased concretes. This paper presents a comprehensive study of the property and performance features including early-age\nisothermal calorimetric response, compressive strength development with time, microstructural features such as the pore volume\nand representative pore size, and accelerated chloride transport resistance of OPC and alkali-activated binder systems. Slag\nmixtures activated using sodium silicate solution (SiO2-to-Na2O ratio or Ms of 1ââ?¬â??2) to provide a total alkalinity of 0.05 (Na2O-tobinder\nratio) are compared with OPC mixtures with and without partial cement replacement with Class F fly ash (20 % by mass) or\nsilica fume (6 % by mass). Major similarities are noted between these binder systems for: (1) calorimetric response with respect to\nthe presence of features even though the locations and peaks vary based on Ms, (2) compressive strength and its development, (3)\ntotal porosity and pore size, and (4) rapid chloride permeability and non-steady state migration coefficients. Moreover, electrical\nimpedance based circuit models are used to bring out the microstructural features (resistance of the connected pores, and\ncapacitances of the solid phase and pore-solid interface) that are similar in conventional OPC and alkali-activated slag concretes.\nThis study thus demonstrates that performance-equivalent alkali-activated slag systems that are more sustainable from energy and\nenvironmental standpoints can be proportioned....
Self-consolidating concrete (SCC) is a stable and cohesive high consistency concrete mix with enhanced filling ability\nproperties that reduce the need for mechanical compaction. Limited standards and specifications have been reported in the\nliterature on the structural behavior of reinforced self-compacting concrete elements. The significance of the research presented in\nthis paper stems from the need to investigate the effect of enhanced fluidity of SCC on the structural behavior of high strength selfconsolidating\nreinforced concrete beams. To meet the objectives of this research, twelve reinforced concrete beams were prepared\nwith two different generations of superplasticizers and designed to exhibit flexure, shear, or bond splitting failure. The compared\nbeams were identical except for the type of superplasticizer being used (second generation sulphonated-based superplasticizer or\nthird generation polycarboxylate-based superplasticizer). The outcomes of the experimental work revealed comparable resistance\nof beam specimens made with self-compacting (SCC) and conventional vibrated concrete (VC). The dissimilarities in the\nexperimental values between the SCC and the control VC beams were not major, leading to the conclusion that the high flowability\nof SCC has little effect on the flexural, shear and bond strengths of concrete members....
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