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This article aims to investigate and optimise the properties of lightweight self-consolidating mortar (LSCM) by using the response surface method (RSM). Silica fume (SF), nano silica (NS), water-cement ratio (W/C) and superplasticiser (SP) were chosen as variables. Also, part of the aggregates was replaced with lightweight expanded clay aggregate (LECA). Due to the advantages of RSM in accommodating multi-response optimisation of LSCM properties, the investigation and analysis were carried out for the stability, segregation and compressive strength. The optimised results recommended acceptable ranges of the required rheological and hardened criteria for LSCM. The mixtures achieved in these ranges include an LSCM with sufficient stability and low segregation. In particular, the results showed that the ultimate segregation must be < 8% for structural concrete. In addition, the results proved that increasing the fraction of NS and SF improves the properties of the LSCM by reducing the segregation and increasing the stability and compressive strength. It was found that adding 6% of NS at a high W/C ratio decreased the segregation by at least 15%. Adding 6% NS and %SF to LSCM within 0.5 W/C increased the compressive strength up to 15.1 MPa for the former and 3.8 MPa for the latter. [ABSTRACT FROM AUTHOR]

Cut off walls are used under dams for the control of sub surfaces seepage and permeability of cut off wall was important. In the construction of cut off walls, plastic concrete is used and the amount of plastic concrete permeability is important. In this study, the permeability of plastic concrete was investigated and the effect of replacing nano silica instead of cement to reduce permeability was studied. So in this research, compressive strength, elastic modulus, and permeability parameters of plastic concrete specimens at different ages (7, 14, 28, and 56 days) and with different percentages of nano silica (0, 1.5, 3, 4.5, and 6%) were investigated. Also, scanning electron microscopy was used to investigate the effect of nano silica on plastic concrete specimens. The results show that as the age of the specimens increases, the compressive strength and elastic modulus increase, and the permeability of the plastic concrete decreases. Also, by adding nano silica to plastic concrete, the compressive strength of the plastic concrete increases and the plastic concrete permeability decreases significantly while its elastic modulus is almost constant. [ABSTRACT FROM AUTHOR]

• Possibility of using industrial waste residue as aggregate in self-consolidating mortars. • Effect of industrial waste residue on the fresh and hardened properties of self-consolidating mortars. • Reduced emissions of heavy metals into concrete by using silica fume. • Reduced compressive strength in the specimens containing industrial waste residue due to disruption in cement hydration. In this research, Industrial Waste Residue (IWR) from sewage treatment plants is used as a substitute for fine aggregates. Nine mix designs with a water to cement ratio of 0.46; and 0, 6, and 10 percent dried industrial waste residue of the Alborz Industrial City in Qazvin as the replacement of fine aggregate; 0, 2, and 4 percent of silica fume; and cement content of 600 kg/m3 are produced. The Mini Slump Flow, Capillary Water Absorption, Compressive Strength, Electrical Resistance, and Toxicity Characteristic Leaching Procedure (TCLP) tests were carried out on the mortar samples to investigate the effect of waste on the performance of the mortar. The results show that the use of this waste as a substitute for fine aggregate strongly reduce the workability of the mortar. In addition, the compressive strength values are reduced by increasing the amount of waste. The highest water absorption is related to samples containing 10% waste and 4% silica fume. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The ranges with sufficient stability and low segregation in the fresh phase are presented. • Mixtures containing silica fume decreased the rheological limitation of EFNARC code. • RSM is an efficient technique for optimizing the properties of the SCM. Abstract Using a high or low amount of cementitious material, water-cement ratio (W/C), and superplasticizer (SP) cause instability and reduction in compressive strength of concrete according to their impact factor and interaction. However, making a concrete with the optimum amount of variables could improve its properties. So, optimization of concrete ingredient due to absence of proper mix design code is required. The remarkable features of response surface method (RSM) are modeling and optimization. This study was carried out with the aim of investigating rheological and hardened properties of self-consolidating mortar (SCM) using RSM with four factors (silica fume, slag, SP and W/C). Rheological criteria of EFNARC code were used to specify the optimum restriction. According to statistical analysis and validation of equations, it can be concluded that RSM is a confident and efficient method to evaluate the properties of SCM. In addition, according to model, the silica fume increased EFNARC code limitation ranges by improving the rheological properties, however, slag had an almost neutral role. In the best case, the addition of silica fume, reduced the segregation up to 5 times. Although silica fume increased the compressive strength up to 45%, slag totally decreased the compressive strength. [ABSTRACT FROM AUTHOR]

The superior performance of Self-Consolidating Concrete (SCC) and Self-Consolidating Mortars (SCMOs) over conventional concrete is generally related to their ingredients. Compared with normal mortar mixtures, the segregation resistance of self-consolidating mortar are more sensitive to small variations of properties such as gradation and moisture content of aggregates, type and dosage of superplasticizer. To study flowability and segregation of SCMOs, it is critical to be able to quickly quantify rheological properties of SCMOs. In this study, to evaluate the fresh properties of self-consolidating mortars, three apparatus (mini column segregation, mini J-ring and mini Orimet tests) have been developed as a simple and fast methods for testing rheological properties of SCMOs. In addition, the limitations of mentioned methods are proposed. The test results were in agreement with the Column Segregation test (ASTM C1610-10), the J-ring test (ASTM C 1621-09), and Orimet test (EFNARC SCC-02). Furthermore, thirty mortar mixtures containing zero to 6 percent nano silica and silica fume are prepared to verify the test methods. The results show that the mixtures containing nano silica and silica fume have higher viscosity than the control mixture. [ABSTRACT FROM AUTHOR]

In recent years, the emergence of nanotechnology and nanomaterial has created hopes to improve various properties of concrete. Nano silica as one of these materials has been introduced as a cement replacement material for concrete mixture in construction applications. It can modify the properties of concrete, due to high pozzolanic reactions and also making a denser microstructure. On the other hand, it is well recognized that the use of mineral admixtures such as silica fume affects the mechanical properties and durability of cementitious materials. In addition, the superior performance of self-consolidating concrete (SCC) and self-consolidating mortars (SCM) over conventional concrete is generally related to their ingredients. This study investigates the effect of nano silica and silica fume on the compressive strength and chloride permeability of self-consolidating mortars. Tests include compressive strength, rapid chloride permeability test, water permeability, capillary water absorption, and surface electrical resistance, which carried out on twenty mortar mixtures containing zero to 6 percent of nano silica and silica fume. Results show that SCMs incorporating nano silica had higher compressive strength at various ages. In addition, results show that nano silica has enhanced the durability SCMs and reduced the chloride permeability. [ABSTRACT FROM AUTHOR]

• The effect of GGBFS and SF in RAC are presented using RSM. • RSM is an efficient method for predicting and optimizing the properties of RAC. • Some equations for prediction of properties of RAC are presented. • The equations provided an excellent correlation between variables and responses. Concrete is the most consumed material in the construction industry, and using recycled concrete aggregates (RCA), silica fume (SF) and ground-granulated blast-furnace slag (GGBFS) in concrete could reduce its negative environmental impacts by preserving natural resources and reducing construction and demolition (C&D) waste generation and CO 2 emissions. Optimizing the mix design based on both mechanical and durability properties of RAC has not been performed. In this study, the mechanical properties and durability of Recycled Aggregate Concrete (RAC) containing GGBFS and Silica Fume (SF) were evaluated via Response Surface Methodology (RSM). The GGBFS was used to reduce the environmental pollution caused by cement production and balancing the negative effect of RA on the mechanical properties of concrete. The results indicated that RA had a negative effect on durability properties of concrete at 7 and 28 ages, while it had no effect on the properties at 90 days. Finally, optimized mix designs were obtained based on two specific scenarios. In the first scenario, the mix design with the highest of both mechanical and durability properties was obtained. In the second one, a mix design with the highest amounts of GGBFS, SF and RA, was achieved, due to the environmental issues related to concrete production. [ABSTRACT FROM AUTHOR]

• Obtaining strength parameter of PC by performing uniaxial and triaxial compressive strength. • Obtaining elastic modulus of PC from stress–strain graph in UU situation. • The effect of confined pressure on the mechanical properties of PC was investigated.Obtaining the shear strength parameter (ø and c) of PC. Plastic concrete is used in the manufacture of cut off wall and its mechanical properties is important for performance of dam. In this paper, in order to investigate the durability and mechanical properties of plastic concrete, uniaxial and triaxial compressive strength tests were performed on plastic concrete specimens in different ages (7, 14, 28, 56 and 90 days) and different percentage of replacement cement by nano silica (0, 1.5, 3, 4.5 and 6%) and compressive strength, the stress–strain behavior, elastic modulus, shear strength parameters of plastic concrete have been evaluated. According to the result, as the age of the specimen increases, elastic modulus, compressive strength and triaxial strength of the plastic concrete enhances. Furthermore, although by increasing the amount of nano silica the strength parameters of plastic concrete are improved and workability of concrete is reduced and the amount of elastic modulus of the specimen is almost constant. The results of shear strength parameters also show that the addition of up to 3% of nano silica increases the cohesion and internal friction angle decreases and with over 3% nano silica this trend is reversed and cohesion decreases and friction angle increases. [ABSTRACT FROM AUTHOR]

In this paper the effect of different binder to solution ratio (B/S) and different Si/Al molar ratio in the synthesis of binary binder based geopolymer paste on their workability, setting and compressive strength is investigated. Geopolymer paste was prepared by combination of metakaolin (MK) and silica fume (SF) as aluminosilicate source with a mixture of sodium hydroxide with concentration of 14M and sodium silicate as alkaline activator solution having constant H 2 O/Na 2 O and Na 2 O/SiO 2 molar ratio. For having different Si/Al ratio, metakaolin has been replaced partially by silica fume in precursor. Workability of fresh paste was measured by mini-slump test. Compressive test at the ages of 1, 3 and 7 days, setting time, FTIR and XRD analysis were used to characterize the geopolymer paste. Results show that the combination of MK and SF can be used as the aluminosilicate source materials for making geopolymer. Also, results concluded both B/S and Si/Al ratios had a significant effect on workability, setting time and strength. By increasing B/S and decreasing Na 2 O/binder ratio in the system the compressive strength increased, also, in constant B/S = 1.2, 1.4 ratio, by increasing Si/Al ratio in binder growth compressive strength was obtained, but in B/S = 1.6, 1.8 with high Si/Al ratio increases, the strength will be reduced. XRD analysis showed that geopolymer has an amorphous to semi-crystalline phase which, by increasing Si/Al ratio, will decrease the intensity of crystalline phases. FTIR spectra results illustrate that when both B/S and Si/Al ratio increase in the system, Si O T bonds will shift to higher wave number. [ABSTRACT FROM AUTHOR]