Effects of dry particle coating with nano- and microparticles on early compressive strength of portland cement pastes

It is known that nano-and microparticles have been very popular in recent years since their advantages. However, due to the very small size of such materials, they have very high tendency to agglomeration particularly for nanoparticles. Therefore, it is critical that they are properly distributed in the system to which they are added. This paper investigated the effects of dry particle coating with nano-and microparticles to solve the agglomeration problem. For a clear evaluation, paste samples were preferred to detemine the compressive strength. Nano-SiO2 and nano-CaCO3, micro-CaCO3 and micro-SiO2, also known as silica fume, were selected as particulate additives. It was studied by the addition of various percentages (0.3, 0.7, 1, 2, 3 and 5%) of nano-and microparticles in cementitious systems, replacing cement by weight with and without dry particle coating. Dry particle coating was made by using a high-speed paddle mixer. Portland cement and additive particles were mixed at 1500 rpm for 30 seconds in high-speed powder mixer designed for this purpose. The 3-day compressive strength of the cement-based samples to which particles were added at the specified rates was determined and the effect of the dry particle coating on the early strength was investigated. According to the results, it was observed that the production of paste with the dry particle coating technique gave higher compressive strength compared to the production of paste directly in early period. Especially with dry particle coating, compressive strength increased more than 100% in paste samples containing 0.3% nano-SiO2 compared to direct addition without coating.

Predictability of concrete damage level by non-destructive test methods

Non-destructive methods have many advantages over traditional test methods, especially since it does not damage the specimen, it can be used multiple times on the same specimen. These advantages also provide a great benefit in terms of following the property development in concrete as the same specimens are used which eliminates the variations related to the specimens. In this study, it is aimed to determine the damaged amount of concrete produced with different binders by electrical bulk resistivity, resonance frequency, and ultrasonic pulse velocity methods. Firstly, concretes containing different binders were produced, and along with the mechanical properties, ultrasonic wave velocity, resonance frequency, and electrical resistivity values of the produced concrete were determined at the 7, 28, and 90 days. Besides, the specimens were subjected to gradually increase compressive loads and non-destructive methods were used to estimate the extent of damage on specimens. It was attempted to establish a relationship between the damage on concrete specimens and the results obtained by non-destructive methods. Consequently, the compressive strength, electrical resistivity, ultrasonic pulse velocity and resonance frequency values of all specimens increased with the advancing age. It was concluded that the resonant frequency method is more successful than other methods in estimating the amount of damage in concrete.

Ballistic strength of aerated concrete

In regional studies conducted by the Law Enforcement Agency and the Armed Forces within the scope of counter-terrorism activities, to ensure peace and security throughout the country and for the police and military personnel to provide security services, the need to produce different solutions has arisen in the face of attacks on the security points established at many important points, especially at the entrance and exit points of the cities. In this context, by changing the direction and angle of the wall types made of aerated concrete used in construction techniques, 7 variations were tested on these wall types with materials formed with adhesive mortar+plaster, monolithic elastomer polyurea, and non-Newtonian fluid, and the strength of these materials were tested with BR6 and BR7 bullets. The main purpose of this study was to determine the most suitable material in terms of security parameters in the shortest time and at a low cost and to create a reliable structure for security cabins. At the end of the study, the best results were obtained with the shots made on the narrow surface of the aerated concrete and the shots made on the platform formed with non-Newtonian fluid.

Strength properties of biopolymer treated clay/marble powder mixtures

Depending on their unique layer structures and chemical structures, soil problems such as swelling, settlement and loss of strength can be seen especially on clay soils when exposed to water. Settlement occurring on clay soils on which the structure is built, causes various damages in the building. Additionally, in the clay soil interacting with water, strength loss occurs due to the effect of the building load. Today, when soil improvement techniques are developed and diversified, clay soils can be stabilized by using different additives. A clay soil that has been improved by adding waste marble powder within the scope of this study in certain percentages (5%, 15%, 25%), biopolymer added clay / marble powder samples were obtained by interacting with locust bean gum in certain percentages (0.5%, 1%, 1.5%). There are many studies in the literature on improving clay soils using only marble powder or only biopolymer. In this study, marble powder and biopolymer were used together and thus, the feasibility of a more effective soil improvement has been investigated. The results showed that the unconfined compressive strength of the biopolymer added clay-marble powder mixtures are higher when compared with natural clay. Similarly, shear box test results showed that the unconsolidated-undrained cohesions and internal friction angles of the doped clay samples increased. It was observed that the strength values of marble powder-added clay increased after improving with biopolymer.

Effect of retardant admixtures type and their using method on the behavior of concrete

Construction sites may be exposed to crisis conditions during the casting process, resulting in delays of several hours and causing destruction of ready-mix concrete. This study suggests an experimental analysis of the possibility of using a specific additional dose of retardant admixtures, which may be used to ready-mix concrete before the initial setting of the concrete occurs. The effect of this additional dose on concrete characteristics in terms of workability, setting time, and compressive strength is also being studied. To conduct this investigation, three types of retardant admixtures from three branded companies were used. In addition, a penetration resistance experiment was conducted on the concrete to determine its setting time. The setting time of concrete was measured at different period intervals depending on when the additional dose of the retardant admixtures was added from the start of the concrete mixing. The results showed that concrete maintained proper workability for a period of more than 5 hours after using the additional dose of retarding admixtures. The additional dose of retarding admixtures not only delayed the concrete setting but also improved the compressive strength of the concrete. This implies that the use of an additional dose of retardant admixtures specifically tailored for ready-mix concrete is an effective option to avoid the return of ready-mixed fresh concrete.

Diffusion study of chloride and binding of water in concrete pore by molecular dynamics simulation using LAMMPS

As for the communication between concrete and the particles, the surface shows Cl− shock and Na adsorption. With expanded particle focus, the solid adsorption capacity for Cl− is upgraded as a result of a detailed overview of the dynamic molecular simulation studies examining the chloride diffusion coefficient. Different characteristics of the diffusion process, including molecular models, system-size effects, temperature, and pressure conditions, and the type of protection, are discussed. This paper focus on Molecular Dynamic Simulation to determine the diffusion coefficient of chloride ion and water molecules in concrete. The diffusion coefficient for NaCl salt obtained 6.60178x10-10m2/s and the diffusion coefficient for CaCl2 salt obtained 7.29305x10-10m2/s. So, the average chloride diffusion coefficient 6.9475x10-10m2/s. Diffusion coefficient obtained from graph 5.562x10-10m2/s. Diffusion coefficients for water molecules for NaCl solution are 6.125x10-10m2/s, 6.85x10-10m2/s, 1.044x10-10m2/s, 8.525x10-10m2/s, 6.25x10-10m2/s. diffusion coefficient of water molecules in CaCl2 solution are 4.5x10-10m2/s, 6.725x10-10m2/s, 1.254x10-10m2/s, 7.725x10-10m2/s, 1.3x10-10m2/s. Average value obtained for water molecule diffusion are 4.545x10-10m2/s, 7.4062x10-10m2/s and 1.149x10-10m2/s. This diffusion of chloride effects the binding of water in concrete pore.

Predicting and comparing the fire performance of a small-scale composite structure

The purpose of this paper is to investigate a strategy for the fire testing of reduced scale structural models which will help engineers design safer structures and reduce the loss from fires. The concept of this work is how composite frame floor arrangements, beam-column connections might be modelled at a small scale suitable for fire testing. Testing full-scale is expensive, besides the testing of scaled model produces reasonable results which help us to understand the failure mechanism and all significant thermo-structural responses involved in a fire. Thermal effects within a structural element generate fire curve, thermal input and structural displacement output, in other words cause and impact. Dimensional analysis, which is a condition for dynamic similarity between prototype and model, can be achieved when all the dimensionless groups are set equal for both model and prototype. On the other hand, scaling rules are used to decide how much insulating material will be used on a structure. 5-storey composite building with composite floors and steel columns has been modelled at small scale with 1/5. The obtained results from various parametric investigations show that the reduced scale model fire test method would be a feasible way to investigate the fire performance of composite structures.

Mechanical strength variation of zeolite-fly ash geopolymer mortars with different activator concentrations

Zeolite is of a significance for geopolymers as it is a natural precursor and does not require additional heat treatment for activation. However, aluminosilicates sourced from natural sources require additional handling for the best use of exploitation. In this study, geopolymers were synthesized by binary use of zeolite and fly ash as main binding material and sodium silicate and sodium hydroxide as alkaline activator. The influence of alkaline activator ratios and sodium hydroxide concentrations on the compressive strength and flexural strength of the zeolite-fly ash based geopolymers were studied. In this research, zeolite-fly ash based geopolymer mortars were produced by using 50% of natural zeolite (clinoptilolite) and 50% of C-type fly ash. Four different activator ratios (Na2SiO3/NaOH: 1, 1.5, 2 and 2.5) and two sodium hydroxide molarities (10M and 12M) was utilized to activate zeolite and fly ash in order to determine the effect of these parameters on the mechanical strengths of the produced geopolymer mortars. The results indicated that as the alkaline activator ratio and NH molarity were increased the compressive strength of the zeolite-fly ash based geopolymers also increased. The maximum compressive and flexural strength values obtained after 28 days of curing were 20.1 MPa and 5.3 MPa respectively and corresponds when used activator ratio of 2.5 and sodium hydroxide concentration of 12 molarity. The obtained results indicated that both the alkaline activator ratio and sodium hydroxide concentration affected the compressive and flexural strengths of zeolite-fly ash based geopolymer mortar specimens.

Mechanical properties and freeze-thaw resistances of bronze-concrete composites

Studies in the literature show that the physical and mechanical properties of concrete could be improved by the incorporation of different kinds of industrial waste, including waste tire rubber and tire steel. Recycling of waste is important for economic gain and to curb environmental problems. In this study, finely ground CuAl10Ni bronze is used to improve the physical and mechanical properties, and freeze-thaw resistances of C30 concrete. The density, cold crushing strength, 3-point bending strength, elastic modulus, toughness, and freeze-thaw resistances of concrete are determined. In addition, the Schmidt Rebound Hammer (SRH) and the ultrasonic pulse velocity (UPV) tests, which are non-destructive test methods, are applied. SEM/EDX analyses are also carried out. It is noted that a more compacted structure of concrete is achieved with the addition of bronze sawdust. Then higher density and strength values are obtained for concretes that are produced by bronze addition. In addition, concretes including bronze sawdust generally show higher toughness due to high plastic energy capacities than pure concrete.

Properties of Portland cement concrete cast with magnetized water: a review

The water utilized in concrete manufacture plays an important role within the concrete mix, beginning from controlling the process of hydration of cement, besides appropriate curing to achieve the required strength, not to mention controlling the workability and durability of the concrete structure. The utmost significant challenge for concrete technology is to improve the properties of concrete. Nowadays, the engineering field needs to produce structures in harmony with the concept of sustainable development through the utilization of high-performance materials with an eco-friendly impact that is produced at a low-cost. The magnetic water (MW) provides one of the utmost towards this objective. The cost of magnetizing water is low because of the simple instruments used and the cost can be adapted to the scale of the work. In the last two decades, a new technology, so-called MW technology, has been extended to use in concrete manufacturing. Therefore, currently, the researchers are interested in the use of MW in the manufacture of cementitious materials helping to rationalize the cement usage and reducing reliance on chemical additives that have a negative environmental impact. Consequently, this paper presents the effect of the magnetization process in the structure of water molecules, the main properties of water. Additionally, the effect of using MW on the fresh and mechanical properties, as well as the durability characteristics and performance of cementitious materials have been reviewed. Moreover, the factors that affect the magnetization process of water, which highlighted discuss in this study. The results revealed that using MW significantly enhances the flowability and the characteristic strengths of cementitious materials as well as the durability properties.