• Advances in concrete construction
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• v.11 no.2
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• pp.141-149
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• 2021

This study is a basic research for evaluating the buildability of cementitious materials for three-dimensional (3D) printing. In the cement paste step, the thixotropy behavior according to the resting time, which represents the time interval between each layer, was analyzed. In addition, the relationship between the thixotropy behavior and 3D concrete printing buildability was derived by proposing a measurement method that simulates the 3D concrete printing buildup process. The analysis of the tendency of the thixotropy behavior according to the resting time revealed that the area of the hysteresis loop (AHyst) showed a tendency to increase and then converge as the resting time increased, which means hysteresis loop approach critical resting time for sufficient buildability. In the thixotropy behavior analysis that simulates the 3D concrete printing buildup process, the buildup ratio, which is the recovery rate of the shear stress, showed a tendency to increase and then converge as the resting time increased, which are similar results like hysteresis loop. It was concluded that AHyst and the buildup ratio can be used as parameters for determining the resting time, and they have close relationships with 3D concrete printing buildability.

• Advances in concrete construction
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• v.11 no.2
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• pp.151-161
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• 2021

The major shortcoming of concrete in most of the applications is its high self-weight and thermal conductivity. The emerging trend to overcome these shortcomings is the use of foam-concrete, which is a lightweight concrete consisting of cement, filler, water and a foaming agent. This study aims at the development of a cost-effective high-volume fly-ash foam-concrete insulation wall cladding for existing buildings using natural fiber like rice straw in different proportions. The paper reports the results of systematic studies on various mechanical, acoustic, thermal and durability properties of foam-concrete with and without replacement of cement by fly-ash. Fly-ash replaces 60 percent by weight of cement in foam-concrete. The water-solid ratio of 0.3, the filler ratio of 1:1 by weight, and the density of 1100 kg/㎥ (approx.) are fixed for all the mixes. Rice straw at 1%, 3% and 5% by weight of cement was added to improve the thermal and acoustic efficiency. From the investigations, it was inferred that the strength properties were increased with fly-ash replacement up to 1% rice straw addition. In furtherance, addition of rice straw and fly-ash resulted in improved acoustic and thermal properties.

• Advances in concrete construction
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• v.11 no.2
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• pp.163-171
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• 2021

This paper studies the effect of using multi-scale reinforcement additives on mechanical strengths, damage performance, microstructure, and water absorption of cementitious composites. Small dosages of carbon nanotubes (CNTs) or polypropylene (PP) microfibers; 0.05%, 0.1%, and 0.2% by weight of cement; were added either separately or simultaneously into cement mortar. The experimental results show the ability of these additives to enhance the mechanical behavior of the mortar. The best improvement in compressive and flexural strengths of cement mortar reaches 28% in the case of adding a combination of 0.1% CNTs and 0.2% PP fibers for compression, and a combination of 0.2% CNTs and 0.2% PP fibers for flexure. Adding CNTs does not change the brittle mode of failure of plain mortar whereas the presence of PP fibers changes it into ductile failure and clearly enhances the fracture energy of the specimens. Scanning electron microscopic (SEM) images of the fracture surfaces highlights the role of CNTs in improving the adhesion between the PP fibers and the hydration products and thus enhance the ability of the fibers to mitigate cracks propagation and to enhance the mechanical performance of the mortar.

• Advances in concrete construction
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• v.10 no.6
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• pp.537-546
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• 2020

Exterior walls in buildings are exposed to various forms of thermal loads, which depend on the positions of walls. Therefore, one of the efficient methods for improving the energy competence of buildings is improving the thermal properties of insulation plaster mortar. In this study, lightweight fine aggregate (LWFA) and micro rubber ash (MRA) from recycled tires were used as partial replacements for sand. The flow ability, unit weight, compressive strength, tensile strength, thermal conductivity (K-value), drying shrinkage and microstructure scan of lightweight rubberized mortar (LWRM) were investigated. Ten mixtures of LWRM were prepared as follows: traditional cement mortar (control mixture); three mixes with different percentages of LWFA (25%, 50% and 75%); three mixes with different percentages of MRA (2.5%, 5% and 7.5%); and three mixes consisting both types with determined ratios (25% LWFA+5% MRA, 50% LWFA+5% MRA and 75% LWFA+5% MRA). The flow ability of the mortars was 22±2 cm, and LWRM contained LWFA and MRA. The compressive and tensile strength decreased by approximately 64% and 57%, respectively, when 75% LWFA was used compared with those when the control mix was used. The compressive and tensile strength decreased when 5% MRA was used. By contrast, mixes with determined ratios of LWFA and MRA affected reduced unit weight, K-value and dry shrinkage.

• Advances in concrete construction
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• v.10 no.6
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• pp.489-498
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• 2020

This paper investigates mechanical properties of roller compacted concrete (RCC) involving reclaimed asphalt pavement (RAP). In this way, a set of 276 cylindrical RCC specimens were prepared with different RAP sizes (i.e., fine, coarse & total) at various ratios (i.e., 10%, 20%, and 40%). Results reveal that incorporation of RAP decreases unconfined compressive strength (UCS), modulus of elasticity (E), and indirect tensile (IDT) strength of RCC. For each RAP size, a regression model was used to maximize RAP content while satisfying the UCS lower limit (27.6 Mpa) mentioned by ACI as a minimum requirement for RCC used in pavement construction. Moreover, UCS of RAP incorporated mixes, dissimilar to that of control mixes, was found to be sensitive and insensitive to the testing temperature and curing time after 7 days, respectively. The results also demonstrate that the higher amounts of RAP, the more flexibility in RCC is. This issue was also proved by the results of modulus of elasticity test. In addition, the toughness index (TI) shows that increase in RAP content leads to up to 43% increase in energy absorbance capacity of RCC.

• Advances in concrete construction
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• v.11 no.1
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• pp.45-58
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• 2021

Experimental investigation has been conducted to study the effect of using Micro/Nano Silica in presence of steel fibers on improving the static response of reinforced concrete beams. Twenty-one mixtures were prepared with micro silica (MS), Nano silica (NS) and steel fibers (SFs) at different percentages. Cement was replaced by 10% and 15% of Micro silica and 1%, 2% and 3% of Nano silica in the presence of steel fibers at different volume fractions 0%, 1%, and 2%. 258 concrete samples, (126 cubes, 63 cylinders, 63 prisms, and six R.C beams), were investigated experimentally in two stages. The first stage was to investigate the mechanical properties of the prepared mixtures. The second stage was to study the static behavior of R.C beams, using the designed concrete mixtures, under a four-point flexural test. The results showed that replacing cement by (10% MS and 1% NS) produces the optimum mix with a significant improvement in the mechanical properties and the response of R.C beams under static loads. In addition, incorporating steel fibers at different volume fractions have a considerable effect on the flexural toughness of concrete mixes.

• Advances in concrete construction
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• v.11 no.1
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• pp.1-9
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• 2021

This article discusses the issue of optimizing controller design issues, in which the artificial intelligence (AI) evolutionary bat (EB) optimization algorithm is combined with the fuzzy controller in the practical application of the building. The controller of the system design includes different sub-parts such as system initial condition parameters, EB optimal algorithm, fuzzy controller, stability analysis and sensor actuator. The advantage of the design is that for continuous systems with polytypic uncertainties, the integrated H2/H∞ robust output strategy with modified criterion is derived by asymptotically adjusting design parameters. Numerical verification of the time domain and the frequency domain shows that the novel system design provides precise prediction and control of the structural displacement response, which is necessary for the active control structure in the fuzzy model. Due to genetic algorithm (GA), we use a hierarchical conditions of the Hurwitz matrix test technique and the limits of average performance, Hierarchical Fitness Function Structure (HFFS). The dynamic fuzzy controller proposed in this paper is used to find the optimal control force required for active nonlinear control of building structures. This method has achieved successful results in closed system design from the example.

• Advances in concrete construction
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• v.11 no.2
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• pp.99-109
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• 2021

Slag blended concrete is widely used as a mineral admixture in the modern concrete industry. This study shows an optimization process that determines the optimal mixture of air-entrained slag blended concrete considering carbonation durability, frost durability, CO2 emission, and materials cost. First, the aim of optimization is set as total cost, which equals material cost plus CO2 emission cost. The constraints of optimization consist of strength, workability, carbonation durability with climate change, frost durability, range of components and component ratio, and absolute volume. A genetic algorithm is used to determine optimal mixtures considering aim function and various constraints. Second, mixture design examples are shown considering four different cases, namely, mixtures without considering carbonation (Case 1), mixtures considering carbonation (Case 2), mixtures considering carbonation coupled with climate change (Case 3), and mixtures of high strength concrete (Case 4). The results show that the carbonization is the controlling factor of the mixture design of the concrete with ordinary strength (the designed strength is 30MPa). To meet the challenge of climate change, stronger concrete must be used. For high-strength slag blended concrete (design strength is 55MPa), strength is the control factor of mixture design.

• Advances in concrete construction
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• v.11 no.2
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• pp.127-140
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• 2021

In this study, twenty-five geopolymer (GP) mixes were prepared by varying the alkaline solids to Metakaolin (MK) and sodium silicate to NaOH ratios from 0.1 to 0.5 and 0.2 to 1.0, respectively, thus giving a wide range of molar ratios of silica to alumina, sodium oxide to alumina and water to sodium oxide. The compressive strength of these GP mixes was determined for four curing schemes involving oven curing at 100℃ for 24 h and three ambient curing with the curing ages of 3, 14, and 28 days. The test results revealed that for the manufacture of GP binder for structural applications of strength up to 90 MPa, the molar ratio of silica to alumina should be greater than 2.3, sodium oxide to alumina should be between 0.6 to 1.2, and water to sodium oxide should not exceed 12. The compressive strength of ambient cured GP mortar gets stabilized at 28 days of ambient curing. Experimental findings were also corroborated by GP microstructure analysis. The embodied energy of MK-based GP mortars, especially of high strength, is significantly less than the cement mortar of equivalent strength.

• Advances in concrete construction
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• v.11 no.3
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• pp.255-260
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• 2021

Vibration of protein microtubules is investigated based upon Orthotropic Elastic Shell Model, considering the effect of thermal stresses. The complete analytical formulas of thermal vibration for microtubules are obtained. It is observed that the effects of thermal stresses on the vibrational frequency mode are more significant when the longitudinal and circumferential wave vectors are large enough. But when the length of wave vector reduces to 5 nm, these effects have no significant effects. The present results well agree with the lattice vibrations of microtubules. Moreover, the results show that the effects of thermal stresses due to small change in temperature are not so significant but with the increase in temperature its effects are obvious.