Showing papers on "Compressive strength published in 2004"

High Mechanical Strength Double‐Network Hydrogel with Bacterial Cellulose

Abstract: Double-network (DN) hydrogels with high mechanical strength have been synthesized using the natural polymers bacterial cellulose (BC) and gelatin. As-prepared BC contains 90 % water that can easily be squeezed out, with no more recovery in its swelling property. Gelatin gel is brittle and is easily broken into fragments under a modest compression. In contrast, the fracture strength and elastic modulus of a BC–gelatin DN gel under compressive stress are on the order of megapascals, which are several orders of magnitude higher than those of gelatin gel, and almost equivalent to those of articular cartilage. A similar enhancement in the mechanical strength was also observed for the combination of BC with polysaccharides, such as sodium alginate, gellan gum, and ι-carrageenan.

Effect of silica fume on mechanical properties of high-strength concrete

Abstract: This paper presents the results of experimental work on short- and long-term mechanical properties of high-strength concrete containing different levels of silica fume. The aim of the study was to investigate the effects of binder systems containing different levels of silica fume on fresh and mechanical properties of concrete. The work focused on concrete mixes having a fixed water/binder ratio of 0.35 and a constant total binder content of 500 kg/m3. The percentages of silica fume that replaced cement in this research were: 0%, 6%, 10% and 15%. Apart from measuring the workability of fresh concrete, the mechanical properties evaluated were: development of compressive strength; secant modulus of elasticity; strain due to creep, shrinkage, swelling and moisture movement. The results of this research indicate that as the proportion of silica fume increased, the workability of concrete decreased but its short-term mechanical properties such as 28-day compressive strength and secant modulus improved. Also the percentages of silica fume replacement did not have a significant influence on total shrinkage; however, the autogenous shrinkage of concrete increased as the amount of silica fume increased. Moreover, the basic creep of concrete decreased at higher silica fume replacement levels. Drying creep (total creep − basic creep) of specimens was negligible in this investigation. The results of swelling tests after shrinkage and creep indicate that increasing the proportion of silica fume lowered the amount of expansion. Because the existing models for predicting creep and shrinkage were inaccurate for high-strength concrete containing silica fume, alternative prediction models are presented here.

Wear resistance and high-temperature compression strength of Fcc CuCoNiCrAl0.5Fe alloy with boron addition

Abstract: This study discusses the wear resistance and high-temperature compression strength of CuCoNiCrAl0.5Fe alloy with various amounts of boron addition. Experiments show that within the atomic ratio of boron addition from x=0 to x=1.0 in CuCoNiCrAl0.5FeBx (referred to as B-0 to B-1.0 alloys), the alloys are of fcc structure with boride precipitation. The volume fraction of borides increases with increasing boron addition. The corresponding hardness increases from HV 232 to HV 736. Wear resistance and high-temperature compression strength are significantly enhanced by the formation of boride. The alloys with boride are less tough. The superior wear resistance of B-1.0 alloy, which is even better than SUJ2 wear-resistant steel, indicates that the CuCoNiCrAl0.5FeBx alloys have potential applications as ambient- and high-temperature mold, tool, and structural materials.

Shear strength model for lightly reinforced concrete columns

Abstract: Parameters affecting the shear strength of reinforced concrete columns having a rectangular cross section and light transverse reinforcement are investigated using data from numerous column tests. A new model is proposed to predict the column shear strength based on theoretical formulations and experimental evidence. The proposed shear strength equation includes contributions from the concrete and transverse reinforcement. Primary parameters in the shear strength model are the column cross-sectional dimensions, concrete compressive strength, column aspect ratio, axial load, and displacement ductility demand. The proposed model is compared with other shear strength models using the available column test data and is shown to result in improved accuracy. A conservative shear strength model for use in design and assessment is proposed based on statistical evaluation of computed and actual shear strengths.

Fundamental Parameters of Cement-Admixed Clay—New Approach

Abstract: The fundamental parameters such as after-curing void ratio (eot) and cement content (Aw) have been found sufficient to characterize the strength and compressibility of cement-admixed clay at high water contents From analyses performed on the results of unconfined compression tests, the ratio eot/Aw has been proven to combine together the influences of clay water content, cement content, and curing time on the strength of cement-admixed clay Moreover, the results of oedometer consolidation tests revealed that while Aw governs the position of the postyield compression line, the magnitude of eot determines the magnitude of the one-dimensional vertical yield stress σvy′ at particular Aw The value of eot reflects, primarily, the clay water content and, secondarily, the cement content and the curing time Normalizing the after-curing unit weight, after-curing water content, and after-curing specific gravity were incorporated in an empirical relationship of eot

Performance of compacted cement-stabilised soil

Abstract: Earth construction is widespread in desert and rural areas because of its abundance and cheap labour and could be an alternative construction material for low cost housing in Algeria. However, earth construction suffers from shrinkage cracking, low strength and lack of durability. This paper reports on the Algerian experience on earth construction in housing and gives an extended review of an experimental study to investigate a stabilised soil by either mechanical means such as compaction and vibration and/or chemical stabilisation by cement. Soil used was characterised by its grading curve and chemical composition. Compaction was either applied statically or dynamically by a drop weight method. A mixture of sand and cement was also tried. The effect of each method of stabilisation on shrinkage, compressive strength, splitting tensile strength and water resistance are briefly reported. The experimental results showed that the best method of stabilisation of the soil investigated, which gives a good compressive strength and a better durability at a reasonable cost, could be a combination of a mechanical compaction and chemical stabilisation by cement or sand and cement up to a certain level.

Hybrid fiber reinforced concrete (HyFRC): fiber synergy in high strength matrices

Abstract: In most cases, fiber reinforced concrete (FRC) contains only one type of fiber. The use of two or more types of fibers in a suitable combination may potentially not only improve the overall properties of concrete, but may also result in performance synergy. The combining of fibers, often called hybridization, is investigated in this paper for a very high strength matrix of an average compressive strength of 85 MPa. Control, single, two-fiber and three-fiber hybrid composites were cast using different fiber types such as macro and micro-fibers of steel, polypropylene and carbon. Flexural toughness tests were performed and results were extensively analyzed to identify synergy, if any, associated with various fiber combinations. Based on various analysis schemes, the paper identifies fiber combinations that demonstrate maximum synergy in terms of flexural toughness.

Atomistic simulations of the yielding of gold nanowires.

Abstract: We performed atomistic simulations to study the effect of free surfaces on the yielding of gold nanowires. Tensile surface stresses on the surfaces of the nanowires cause them to contract along the length with respect to the bulk face-centered cubic lattice and induce compressive stress in the interior. When the cross-sectional area of a (100) nanowire is less than 2.45 nm x 2.45 nm, the wire yields under its surface stresses. Under external forces and surface stresses, nanowires yield via the nucleation and propagation of the {l_brace}111{r_brace} partial dislocations. The magnitudes of the tensile and compressive yield stress of (100) nanowires increase and decrease, respectively, with a decrease of the wire width. The magnitude of the tensile yield stress is much larger than that of the compressive yield stress for small (100) nanowires, while for small nanowires, tensile and compressive yield stresses have similar magnitudes. The critical resolved shear stress (RSS) by external forces depends on wire width, orientation and loading condition (tension vs. compression). However, the critical RSS in the interior of the nanowires, which is exerted by both the external force and the surface-stress-induced compressive stress, does not change significantly with wire width for same orientation andmore » same loading condition, and can thus serve as a 'local' criterion. This local criterion is invoked to explain the observed size dependence of yield behavior and tensile/compressive yield stress asymmetry, considering surface stress effects and different slip systems active in tensile and compressive yielding.« less