• Computers and Concrete
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• 제20권2호
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• pp.145-154
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• 2017

In geological engineering, grouting with Portland cement is a common technique for ground improvement, during which micro-fine cement is applied as a slurry, such that it intrudes into soil voids and decreases soil porosity. To determine the utility and behavior of cements with different Blaine values (index of cement particle fineness) for stabilization of fine sand, non-destructive and destructive tests were employed, such as laser-ray determination of grain size distribution, and sedimentation, permeability, and compressive strength tests. The results of the experimental study demonstrated a suitable mix design for the upper and lower regions of the cement-grading curve that are important for grouting and stabilization. Increasing the fineness of the cement decreased the permeability and increased the compressive strength of grouted sand samples considerably after two weeks. Moreover, relative to finer (higher Blaine value) or coarser (lower Blaine value) cements, cement with a Blaine value of $5,100cm^2/g$ was optimal for void reduction in a grouted soil mass. Overall, study results indicate that cement with an optimum Blaine value can be used to satisfy the designed geotechnical criteria.

• Computers and Concrete
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• 제21권3호
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• pp.311-319
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• 2018

This study used a volumetric method for design. The control group used waste Liquid Crystal Displayplay (LCD) glass powder to replace cement (0%, 10%, 20%, 30%), and the PZT group used Pd-Zr-Ti piezoelectric (PZT) powder to replace 5% of the fine aggregate to make cement mortar. The engineering and the mechanical and electricity properties were tested; flow, compressive strength, ultrasonic pulse velocity (UPV), water absorption and resistivity (SSD and OD electricity at 50 V and 100 V) were determined; and the correlations were determined by linear regression. The compressive strength of the control group (29.5-31.8 MPa) was higher than that of the PZT group (25.1-29 MPa) by 2.8-4.4 MPa at the curing age of 28 days. A 20% waste LCD glass powder replacement (31.8 MPa) can fill up finer pores and accelerate hydration. The control group had a higher 50 V-SSD resistivity ($1870-3244{\Omega}.cm$), and the PZT group had a lower resistivity ($1419-3013{\Omega}.cm$), meaning that the resistivity increases with the replacement of waste LCD glass powder. This is because the waste LCD glass powder contains 62% $SiO_2$, which is a low dielectric material that is an insulator. Therefore, the resistivity increases with the $SiO_2$ content.

• Computers and Concrete
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• 제21권2호
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• pp.139-147
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• 2018

Due to enhanced construction requirement, ready mixed concrete are being popular day by day. The current study aimed to develop ready mixed concrete using GBFS contained cement and determine its properties of fresh and hardened states. A real scale experiment was set up in a ready mixed plant for measuring workability and compressive strength. The workability was tested after mixing (within 5 minutes), 30, 60, 90, 120 and 150 minutes of the running of bulk carrier. The ready mixed carrier employed spinning motion i.e., rotating around its axis with 20 RPM and running on road with 1km/h speed. The mixing ratio of cement: sand:gravel, water to cement ratio, super plasticizer were, 1:1.73:2.47, 0.40 and 6% of cement, respectively. The chemical composition of raw material was determined using XRF and the properties of cements were measured according to ASTM standards. The experimental results confirm that the cement with composition of 6.89% of GBFS, 4% of Gypsum and 89.11% of clinker showed the good compressive strength and workability of concrete after 150 minutes of the spinning motion in bulk carrier.

• Computers and Concrete
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• 제9권2호
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• pp.153-169
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• 2012

The contribution of steel fibers on the 28-day compressive strength of high-performance steel fiber reinforced concrete was investigated, is presented. An extensive experimentation was carried out over water-cementitious materials (w/cm) ratios ranging from 0.25 to 0.40, with silica fume-cementitious materials ratios from 0.05 to 0.15, and fiber volume fractions ($V_f$= 0.0, 0.5, 1.0 and 1.5%) with the aspect ratios of 80 and 53. Based on the test results of 44 concrete mixes, mathematical model was developed using statistical methods to quantify the effect of fiber content on compressive strength of HPSFRC in terms of fiber reinforcing index. The expression, being developed with strength ratios and not with absolute values of strengths, is independent of specimen parameters and is applicable to wide range of w/cm ratios, and used in the mix design of steel fiber reinforced concrete. The estimated strengths are within ${\pm}3.2%$ of the actual values. The model was tested for the strength results of 14 mixes having fiber aspect ratio of 53. On examining the validity of the proposed model, there exists a good correlation between the predicted values and the experimental values of different researchers. Equation is also proposed for the size effect of the concrete specimens.

• Computers and Concrete
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• 제26권2호
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• pp.115-125
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• 2020

To reduce the damage of concrete in fire, a new type of lightweight cinder aggregate concrete was developed due to the excellent fire resistance of cinder. To further enhance its fire resistance, Polypropylene (PP) Fibers which can enhance the fire resistance of concrete were also used in this type of concrete. However, the bond behavior of this new type of concrete after fire exposure is still unknown. To investigate its bond behavior, 185 specimens were heated up to 22, 200, 400, 600 or 800℃ for 2 h duration respectively, which is followed by subsequent compressive and tensile tests at room temperature. The concrete-rebar bond strength of C30 PP fiber-reinforced cinder concrete was subsequently investigated through pull-out tests after fire exposure. The microstructures of the PP fiber-reinforced cinder concrete and the status of the PP fibre at different temperature were inspected using an advanced scanning electron microscopy, aiming to understand the mechanism of the bonding deterioration under high temperature. The effects of rebar diameter and bond length on the bond strength of PP fiber-reinforced cinder concrete were investigated based on the test results. The bond-slip relation of PP fiber-reinforced cinder concrete after exposure at different temperature was derived based on the test results.

• Computers and Concrete
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• 제26권2호
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• pp.137-150
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• 2020

In this paper, the bending behavior of single-walled carbon nanotube-reinforced composite (CNTRC) laminated plates is studied using various shear deformation plate theories. Several types of reinforcement material distributions, a uniform distribution (UD) and three functionally graded distributions (FG), are inspected. A generalized higher-order deformation plate theory is utilized to derive the field equations of the CNTRC laminated plates where an analytical technique based on Navier's series is utilized to solve the static problem for simply-supported boundary conditions. A detailed numerical analysis is carried out to examine the influence of carbon nanotube volume fraction, laminated composite structure, side-to-thickness, and aspect ratios on stresses and deflection of the CNTRC laminated plates.

• Computers and Concrete
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• 제17권5호
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• pp.639-653
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• 2016

The present article discusses the effect of the ratio of bridge surface to total shear surface, number of bridge areas and normal stress on the failure behavior of the planar non-persistent open joints. Totally, 38 models were prepared using plaster and dimensions of $15cm{\times}15cm{\times}15cm$. The bridge area occupied $45cm^2$, $90cm^2$ and $135cm^2$ out of the shear surface. The number of rock bridges increase in fixed area. Two similar samples were prepared on every variation in the rock bridges and tested for direct shear strength under two high and low normal loads. The results indicated that the failure pattern and the failure mechanism is mostly influenced by the ratio of bridge surface to total shear surface and normal stress so that the tensile failure mode change to shear failure mode by increasing in the value of introduced parameters. Furthermore, the shear strength and shear stiffness are closely related to the ratio of bridge surface to total shear surface, number of bridge areas and normal stress.

• Computers and Concrete
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• 제6권2호
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• pp.133-153
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• 2009

Discrete element modeling (DEM) in concrete technology is concerned with design and use of models that constitute a schematization of reality with operational potentials. This paper discusses the material science principles governing the design of DEM systems and evaluates the consequences for their operational potentials. It surveys the two families in physical discrete element modeling in concrete technology, only touching upon probabilistic DEM concepts as alternatives. Many common DEM systems are based on random sequential addition (RSA) procedures; their operational potentials are limited to low configuration-sensitivity features of material structure, underlying material performance characteristics of low structure-sensitivity. The second family of DEM systems employs concurrent algorithms, involving particle interaction mechanisms. Static and dynamic solutions are realized to solve particle overlap. This second family offers a far more realistic schematization of reality as to particle configuration. The operational potentials of this family involve valid approaches to structure-sensitive mechanical or durability properties. Illustrative 2D examples of fresh cement particle packing and pore formation during maturation are elaborated to demonstrate this. Mainstream fields of present day and expected application of DEM are sketched. Violation of the scientific knowledge of to day underlying these operational potentials will give rise to unreliable solutions.

• Computers and Concrete
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• 제25권3호
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• pp.215-224
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• 2020

In the present study, according to the important of porosity in low specific weight in comparison of high stiffness of carbon nanotubes reinforced composite, buckling and free vibration analysis of sandwich composite beam in two configurations, of laminates using differential quadrature method (DQM) is studied. Also, the effects of porosity coefficient and three types of porosity distribution on critical buckling load and natural frequency are discussed. It is shown the buckling loads and natural frequencies of laminate 1 are significantly larger than the results of laminate 2. When configuration 2 (the core is made of FRC) and laminate 1 ([0/90/0/45/90]_s) are used, the first natural frequency rises noticeably. It is also demonstrated that the influence of the core height in the case of lower carbon volume fractions is negligible. Even though, when volume fraction of fiber increases, the critical buckling load enhances smoothly. It should be noticed the amount of decline has inverse relationship with the beam aspect ratio. Investigating three porosity patterns, beam with the distribution of porosity Type 2 has the maximum critical buckling load and first natural frequency. Among three elastic foundations (constant, linear and parabolic), buckling load and natural frequency in linear variation has the least amount. For all kind of elastic foundations, when the porosity coefficient increases, critical buckling load and natural frequency decline significantly.

• Journal of Pharmaceutical Investigation
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• 제31권1호
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• pp.1-5
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• 2001

The aggregation behavior of nystatin (NYS) in the presence of pluronic F127, triblock copolymer of poly (ethylene oxide) (PEO) and poly (propylene oxide) (PPO), was measured and correlated with hemolytic activity. Antifungal activity was also studied using Saccharomyces cerevisiae as a model strain. The critical aggregation concentrations (CAC) of the drug were 50.1, 108.0, 134.2, 154.3, and $217.9\;{\mu}M$ at 0.1%, 0.5%, 1.0%, 1.5%, and 2.0% pluronic F127 solution, respectively. The levels of NYS required to start lysis of erythrocytes were about 80, 100, 125, 150, and $200\;{\mu}M$ at 0.1%, 0.5%, 1.0%, 1.5%, and 2.0% pluronic F127 solution, respectively. It was $50\;{\mu}M$ in the absence of the polymer. Minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) of NYS-pluronic F127 lyophilizate were same at $3\;{\mu}g/ml$, while MIC and MFC of pure NYS are $3\;{\mu}g/ml$ and $12\;{\mu}g/ml$, respectively. By modulating the aggregation behavior of NYS, pluronic F127 was able to reduce the toxicity of the drug without compromising the MIC and MFC.