Mechanism Of Strength Development Research Articles

에코시멘트 콘크리트의 장기강도 특성 및 성능 향상 방안에 관한 연구

Concrete using eco-cement has a problem with long-term strength development. However, currently, a long-term strength development mechanism is not confirmed, resulting in a lack of application of eco-cement in construction fields. In this study, the curing humidity influence on development in long-term strength of concrete using eco-cement and the relationship between strength and pore structure were examined. The results showed that wet cured eco-cement with a high water/cement ratio showed serious long-term strength reduction due to non-reduction of pore volume (pore size over 10 nm) in mortar caste with eco-cement. Also, the study results on improvement of long-term strength of eco-cement by partial replacement with ordinary portland cement and finely-ground fly ash showed that both of these alternatives improved long-term strength of concrete caste with eco-cement due to gradual refinement of their micro-structure.

Analysis of geopolymer concrete columns

Ordinary portland cement (OPC) has been traditionally used as the binding agent in concrete. However, it is also necessary to search for alternative low-emission binding agents for concrete to reduce the environmental impact caused by manufacturing of cement. Geopolymer, also known as inorganic polymer, is one such material that uses by-product material such as fly ash instead of cement. Recent research has shown that fly ash-based geopolymer concrete has suitable properties for its use as a construction material. Since the strength development mechanism of geopolymer is different from that of OPC binder, it is necessary to obtain a suitable constitutive model for geopolymer concrete to predict the load–deflection behaviour and strength of geopolymer concrete structural members. This article has investigated the suitability of using an existing stress–strain model originally proposed by Popovics for OPC concrete. It is found that the equation of Popovics can be used for geopolymer concrete with minor modification to the expression for the curve fitting factor, to better fit with the post-peak parts of the experimental stress–strain curves. The slightly modified set of stress–strain equations was then used in a non-linear analysis for reinforced concrete columns. A good correlation is achieved between the predicted and measured ultimate loads, load–deflection curves and deflected shapes for 12 slender test columns.

シリカフューム混合セメントの各種養生条件における水和反応の違いとＲＰＣの超高強度発現メカニズムの推定

Two-component mortar paste consisting of cement and silica fume was cured in water or steam, and its strength development, cement hydration capacity and silica fume reaction rate were analyzed to identify the role of the admixture, determine the optimum curing condition for RPC containing silica powder and estimate its high strength development mechanism. The total silica fume reaction amount calculated by multiplying the added amount by the reaction rate increased with more silica fume added. Ca/Si ratio of generated C-S-H was about 0.7 at the lowest, suggesting a mixed phase of C-S-H and silica gel. RPC is known that inclusion of silica powder of intermediate sizes increases particle compaction. The low Ca/Si C-S-H with silica gel was considered to further bridge voids between particles firmly, thereby resulting in ultra high strength of RPC.

Mechanical Properties of Polyester Polymer Concrete Using Recycled Polyethylene Terephthalate

If unsaturated polyester based on recycled polyethylene terephthalate (PET) is properly formulated, it can be mixed with inorganic aggregates to produce polymer concrete with very high mechanical properties and durability performance. Despite the low manufacturing cost from plastic wastes, polymer concrete precast components are not popular in building panels, junction boxes, flow drains, trench lines, and transportation-related components because the time-dependent strength development mechanism and mechanical properties are still far from being fully understood. The objective of this paper is to investigate the mechanical properties such as the compressive strength, the splitting tensile strength, and the flexural strength of polymer concrete using an unsaturated polyester resin based on recycled PET. The relationships between the mechanical properties are analyzed. The polymer concrete using resin based on recycled PET can achieve compressive strength of 73.7 MPa, flexural strength of 22.4 MPa, splitting tensile strength of 7.85 MPa, and elastic modulus of 27.9 GPa, at 7 days. Some relationships exist between the compressive strength of polymer concrete and other properties (elastic modulus, flexural strength, and splitting tensile strength). The use of recycled PET in polymer concrete helps in reducing the cost of the material, solving some of the solid waste problems posed by plastics, and saving energy.

Optimum Silica Fume Content and Its Mode of Action on Concrete

The aim of this paper is to develop a better understanding of the isolated contribution of silica fume on concrete and determine its optimum content. There is much debate among researchers as to the mode of action of silica fume on the mechanism of strength development and its optimum replacement percentage. Extensive experimentation was conducted over water-binder ratios ranging from 0.26-0.42 and silica fume-binder ratios from 0.0-0.3. Results indicate that the optimum replacement percentage for 28-day strength is not a constant one, but depends on the water-cementitious material ratio of the mixture and has been found to range from 15-25%. On quantifying the pozzolanic and physical effects of silica fume, it is observed that both mechanisms significantly contribute to the concrete strength.

Strength development at low temperatures in coal ash deposits

At temperatures below approximately 1900°F, ash particles formed in coal-fired energy systems are relatively hard and not prone to sticking to system surfaces. However, if the ash collects on a surface not exposed to a shearing gas flow such as the downstream side of a heat exchanger or the surface of a hot-gas filter, the deposit can develop enough strength over a period of minutes to days so that it becomes difficult to remove, in some cases growing to sizes that impede the flow of gas. This paper presents data from ongoing measurements of the significance of ash and gas composition, deposit temperature, and time on the rates of strength development in simulated low-temperature ash deposits. Preliminary results of surface composition and particle-size distribution analyses of the ash, including submicron material, are also presented to explain the possible mechanisms of strength development.

Stress‐strain behavior of surficial carbonate sediments from key west, Florida, USA

A triaxial strength testing program was conducted to determine the stress strain and strength behavior of a surficial calcareous sediment from the Dry Tortugas study site west of Key West, Florida, which is part of the Coastal Benthic Boundary Layer Special Research Program. The sediment at the study site is comprised largely of Halimeda algal grains resulting in carbonate contents near 93% by mass. Sediment grains range from sand‐sized shells and shell fragments to carbonate muds. Isotropically consolidated undrained triaxial tests were conducted at consolidation stresses no greater than 34 kPa on undisturbed and remolded sediment samples from box cores. It was found that the sediments behave like a loose sand during shear and are characterized by failure envelopes with friction angles between 37° and 39° with no cohesive intercepts. Initial elastic tangent Young's moduli, determined by the hyperbolic method, range from 130 kPa to 18,873 kPa, and exponential relations between the elastic moduli and confining stress are found to exist for the undisturbed and remolded sediments. Particle size distributions were found for the sediments at various stages of testing and results show that no particle crushing occurred due either to the stresses or the remolding procedures employed in this investigation. Although apparent overconsolidation was present, there was no evidence of cementation during shear, as a brittle failure mechanism was not present. Comparisons of the strength behavior of the undisturbed and remolded sediments suggest that particle mobility plays an important role as a mechanism of strength development.

The influence of phosphate on the properties of clay bricks

The fabrication, properties and composition of heated phosphate-bonded clay bricks are reported. The strength of phosphate-bonded clay bodies is shown to be related to the equilibrium pH of the clay mix. The highest strengths were obtained for mixes with equilibrium pH 7 fired at 500°C which gave a modulus of rupture 60% higher than the unmodified clay heated under similar conditions but at 800°C firing temperature. The phosphate-bonded products were also of low porosity and improved dimensional stability. An insight into the probable mechanism of strength development of the heated product has been obtained from XRD, SEM and DSC studies. The results show that the properties of the phosphate-bonded clay bodies are critically affected by new mineral phases resulting from the reactions of phosphates with clay which subsequently undergo physico-chemical changes above 550°C.

人工配合した中間土の強度発現機構に関する実験的研究

In order to make clear the strength development mechanism of intermediate soils, the direct shear tests were performed on artificially mixed soils to examine the influences of soil texture and consolidation pressure. The following conclusions were obtained:(1) The shear strength characteristic of soils changes from that of sand to clay with increasing clay content and from that of clay to sand with increasing consolidation pressure.(2) From the direct shear tests, the experimental constant cσc characterizing the boundary between sand and clay was found to exist and vary with the clay content and consolidation pressure.(3) The expreimental constant cσcn characterizing the soil properties was also found.

A STUDY ON THE RELATIONSHIP BETWEEN STRENGTH AND PORE SIZE DISTRIBUTION IN COMPACTED STABILIZED SOILS

Recently, chemical soil stabilizations are actively adopted for the improvement of the soft ground on which roads or buildings will be constructed. In addition to traditional stabilizers of Poltland cement and lime, the industrial by-products such as fly ash and pulverized blastfurnace slag are also used for the purpose of increasing the effectiveness of cement and lime as a stabilizer and their effective utilization in soil stabilization. The objective of this study is to reveal the mechanisms of strength development of the compacted stabilized soils from a microstructural view-point. The compressive strength, modulus of deformation and pulse velocity of various compacted soils stabilized with cement, lime and lime-fly ash (or pulverized blastfurnace slag) were measured. Their microstructures were also characterized by the SEM observation and pore size distributions obtained by the mercury intrusion porosimeter. The relationships between strength and changes in microstructure in compacted stabilized soils are discussed.

深層混合安定処理土の強度と微視的構造

Recently, chemical soil stablization using the deep mixing method has been actively adopted for the improvement of soft ground in the offshore regions. The objective of this study is to reveal the mechanism of strength development in the uncompacted stabilized soils made by the deep mixing method. The mechanical properties such as strength, modulus of deformation and pulse velocity of the solis stabilized by cement or lime-blastfurnace slag were comparatively investigated. Furthermore, the reaction process and microstructure in them were elucidated by X-ray diffraction, SEM observation and the measurement of pore size distributions. From these results, the relationship between strength development and change in microstructure in the uncompacted stabilized soils was discussed.

Modeling the development of strength in pellets

Mathematical models used for describing the heat hardening of iron-ore pellets should include a description of the development of fired strength. This paper reviews the mechanisms of strength development and presents a suitable formalism for strength development that can be used in mathematical models. The formalism is shown to adequately fit experimental results generated under laboratory conditions where the time-temperature profiles of the pellets are known.

Mechanism of strength development of cement-treated soil: Tatsuro Muro, Meiketsu Enoki, Soichiro Kawahara

Mechanism of strength development of cement-treated soil: Tatsuro Muro, Meiketsu Enoki, Soichiro Kawahara