Cement-based Concrete Research Articles

EFFECT OF GRAPHENE OXIDE ON THE MECHANICAL STRENGTH AND MICROSTRUCTURE OF CEMENTITIOUS MATERIALS

Cement-based concrete is used commonly for numerous constructions. Even though, cement has superior properties and great performance, its inherited brittleness is a major setback that needs more investigation for improvement. To eliminate this problem different types of additives, fibers, supplementary cementitious materials and nanomaterials have been used. One of these promising nanomaterials is graphene. This study is to investigate the feasibility of using graphene as a nano-additive to the cement based materials combined with a common used nano-additive such as silica fume as a dispersant. To conduct the study, eleven different mortar mixes were cast to investigate microstructure and mechanical properties of the cement mortar materials which were compared to benchmark samples. The studied parameters were ratios of both silica and graphene. Based on compressive and tensile strength, the results show that graphene can be thought of having the potential to be used as nano-reinforcement to improve the mechanical properties of cement based materials, provided that a proper amount of the dispersion agent is used.

Synthesis and characterization of fly ash and slag based geopolymer concrete

This paper presents the formulation and characterization of composite fly ash and slag based geopolymer concrete. Potassium hydroxide (KOH) and potassium silicate (K2SiO3) liquid alkaline activators were used in the preparation of the geopolymer concrete. The mechanical response of the best recipe was investigated through compressive, tensile and flexural strength tests after 3, 7 and 28 days of curing. One batch was tested for compressive strength after 16 and 32 weeks of curing. The microstructure of the concretes was characterized using scanning electron microscopy (SEM). The testing results are compared with a reference ordinary portland cement-based concrete. After 28 days of curing, test results showed that the geopolymer concretes can approach the compressive strength of the reference ordinary concrete. Moreover, the tensile strength and flexural strength attained reached up to 68% and 80% of the reference cement, respectively. The results indicated the potential application of geopolymer that can satisfy the standard strength requirement. After longer time of curing, 32 weeks, some of the geopolymer preparations exhibited 111% compressive strength, compared to the ordinary cement reference.

The effect of open-air curing on compressive strength of geopolymer mortar containing laterite soil and slaked lime

Most surface layers in the Papua and Kalimantan regions are Laterite Land. When dry lateritic soil dries but when containing large amounts of water, laterite soil becomes overtime. Cement production requires a lot of energy so that geopolymer concrete and mortar is a material that has great potential as an alternative to reduce the use of Portland cement because it has mechanical properties that almost resemble Portland cement-based concrete. This study discusses the use of fly ash and alkali activator (NaOH and Na2SiO3) to bind laterite soil by adding quenched lime to reduce the use of ovens to form geopolymer mortar. Comparison of laterite and lime outages is used, namely 95%: 5% and 90%: 10%. Testing of the flow of fresh geopolymer mortar shows that all materials can be bonded well and no segregation occurs. The hardened test material is treated in air-exposed for 3, 7 and 28 days. Testing of compressive strength was analyzed to determine the behavior of geopolymer mortar. The test results showed that there was an increase in compressive strength from the age of 3 to 7 days but decreased at the age of 28 days due to rainy weather, sunlight which resulted in the specimen experiencing flowers (during rain) and shrinkage (during hot weather) so that cracks occurred cracks in specimens, as well as the use of comparison of laterite and lime soils, extinguished 90%: 10% resulting in better compressive strength compared to the use of the ratio of laterite and lime outages of 95%: 5%.

Synthesis of nanosilica from fly ash and its utilization with lime sludge in concrete: an environmentally friendly and sustainable solution

Solid waste generation and its disposal is becoming the cause of concern all over the world. Paper industry is not exceptional as lime sludge and fly ash need appropriate utilization to reduce the threat for the environment. Application of these materials in other industries could be the appropriate alternative. In this paper, fly ash is utilized for nanosilica synthesis, because of the presence of silica precursor in very high amount. Nanosilica was synthesized with the alkali treatment of ash and acid precipitation. The produced nanosilica was characterized for crystallinity, specific surface area, size and morphology. This synthesized nanosilica is used with lime sludge in cement-based concrete. Concrete blocks were evaluated for compressive strength after 7 and 28 days of curing. It is observed that the compressive strength of concrete blocks with only lime sludge decreased up to 50% with the replacement of cement by lime sludge from 10 to 40%. Concrete blocks produced with the addition of 0.3, 0.6 and 1.0% nanosilica and different proportions of lime sludge attained up to 30% more compressive strength in comparison with the blocks without nanosilica.

Evaluation of Engineering Properties of Calcium Sulfoaluminate Cement-based Concretes Reinforced with Different Types of Fibers.

Calcium sulfoaluminate (CSA) cement has recently gained increased attention due to its lower amount of CO2 emissions, as compared to that of the ordinary Portland cement (OPC). This paper evaluates the impact of different types of fibers on the engineering features of CSA-based concretes at different water-cement ratios of 0.35 and 0.28. In this study, metallic fibers including double hooked-end steel fibers and hooked-end steel fibers, and non-metallic fibers (i.e., polyvinyl alcohol (PVA) fibers) were utilized at fiber content of 1%. The mechanical properties of concretes were assessed at different curing ages. Dimensional stability of the concrete mixes was also examined. The morphology of the fractured specimens was studied by using the SEM method. The results indicate that the engineering properties of concrete were improved by introducing fibers to the concrete, irrespective of fiber type. The results show that DHE steel fiber has an important effect on the flexural performance of CSA cement-based concretes and results in deflection-hardening behavior. It was observed that fibers and particularly PVA fibers cause a decrease in shrinkage deformation. Microstructure tests demonstrate that prismatic ettringite is the main hydration product of CSA cement-based concrete. The SEM observation also confirms that the inclusion of CSA cement in concrete improves the cohesiveness between the fibers and cement matrix.

Shear strength of fly ash-based geopolymer reinforced concrete beams

Geopolymer concrete (GC) is a synthetic material that combines sustainability and appropriate engineering properties, and it is relatively cost-effective compared to Portland cement-based concrete, its traditional competitor. Most GC studies have analyzed the microstructure and the chemical composition of GC. However, studies on the structural behavior of GC are limited. Thus this research focuses on the shear behavior of fly ash-based GC beams. Four GC beams and one conventional concrete beam were experimentally investigated to determine their shear strengths. The test variables included the shear span-to-effective depth ratio and the transverse reinforcement ratio of the investigated beams. The strength, strains, deformations, and mode of failure of the investigated beams are presented. The shear strengths of the investigated beams are comparable to those of conventional concrete beams.

Fuzzy dynamics of multibody systems with polymorphic uncertainty in the material microstructure

This paper deals with the fuzzy dynamics of multibody systems with polymorphic uncertainty in the material microstructure. Macroscopic material properties are obtained using fuzzy-stochastic FEM based computational homogenization. In particular, the spectral stochastic local FEM is utilized to simulate a representative volume element of the microstructure. Forward dynamics of the macroscopic system is modeled using the Graph Follower algorithm. Thereby we propagate the uncertainty from the lowest level of material microstructure to the highest level of multibody dynamics. Differences in the propagation of epistemic and aleatoric uncertainties to the macroscale and their influence on the multibody dynamics are discussed. A particular example of a multibody system used in this paper is a multistory frame, whereby the considered heterogeneous material is a cement-based concrete.

Mitigating the Risk of Early Age Cracking in Fly Ash Blended Cement-Based Concrete Using Ferronickel Slag Sand

Mitigating the Risk of Early Age Cracking in Fly Ash Blended Cement-Based Concrete Using Ferronickel Slag Sand

Synthesis and Characteristics of Local Fly Ash Based Geopolymers Mixed with Natural Aggregates

Global industrialization generates large amount of waste which strongly affects the depositing areas and the living creatures from the surroundings. In the same time, the construction sector meets an exponential development process, resulting in materials and construction areas increase. Therefore, the need of new materials was felt worldwide. One solution that knew a rapid development, especially in this sector, was to obtain new eco-friendly materials through a mechanism called geopolymerization. True this powerful chemical reaction between a waste, rich in aluminum and silicon, and a strong alkaline solution, a tetragonal structure of Al-O-Si is obtained that possess properties comparable to those of Portland cement-based concrete. In the present paper the effect of aggregates on local fly ash based geopolymers is analyzed from the structure and mechanical properties point of view. According to this study, the aggregates strongly influence the density, compression strength and flexural strength at any age of samples.

Research into the protective characteristics of special-purpose cement-based concretes

Research into the protective characteristics of special-purpose cement-based concretes

Mechanical properties of high ductile magnesium oxychloride cement-based composites after water soaking

Applications of magnesium oxychloride cement-based concrete in civil engineering are limited due to material's poor water resistance and inherent brittleness. For improvement, a new kind of material, magnesium oxychloride cement-based engineered cementitious composite (MOC-ECC), was developed. This paper introduces the effects of fly ash and polyethylene fibers incorporations on the fluidity, tensile behavior and compressive properties of MOC-ECC. The test results indicated that MOC-ECC exhibits outstanding strain hardening and multi-cracking characteristics with tensile strain capacity up to 8% and tensile strength over 7 MPa. More importantly, to explore the combined influences of fly ash and polyethylene fiber on the water resistance of MOC-ECC, XRD and SEM were used to analyze the variations of chemical composition and microstructure, and three-point bending test and single crack tension test were conducted to obtain the fracture toughness and fiber bridging capacity, respectively. An explanation to the mechanisms of the enhanced mechanical property and water resistance is presented at microscopic and mesoscopic scales.

Strength and fracture analysis of polymer-granular matter composites at variable weight percent ratio

In this study, the optimal weight percent ratio of resin and aggregate for a polymer-granular matter composite (PGMC) was determined in terms of its compressive strength. The PGMC was made with polyester for its resin, and white sand as its aggregate. The weight percent ratios of the PGMC varied as follows: 15:85, 20:80, and 25:75 for resin and aggregate respectively. The PGMC specimens underwent a compression test after a curing period of seven days at room temperature to determine its compression strength. Results indicate that the PGMC with weight percent ratio 25:75 had the highest average compression strength out of the three types at 76.4 MPa which is more than twice the strength of cement-based concrete. The 15:85 and 20:80 PGMCs yielded average compression strengths of 19.8 MPa and 60.8 MPa respectively. The most common fracture type for the PGMCs having weight percent ratios 20:80 and 25:75 was shear, occurring 83.3% of the time. On the other hand, the PGMC having weight percent ratio 15:85 displayed shear wedge fracture for five of the six trials.

RETRACTED: Thermal shock reactions of Ordinary Portland cement and geopolymer concrete: Microstructural and mechanical investigation

Abstract Thermal shock resistivity is one of the most important characteristics of the concrete. There are numerous research papers, which investigate the reduction of fundamental engineering properties after Ordinary Portland cement (OPC) is subjected to thermal shock. In consequence to this functional disadvantage of OPC, this study explores the post thermal shock behaviour of geopolymer concrete constructed from Gladstone fly ash compared to Ordinary Portland cement-based concrete by means of rapid water to air-cooling after being heated to temperatures of 400 °C, 600 °C, 800 °C and 1000 °C. Specimens were analysed via the use of the universal testing machine, scanning electron microscopy, X-ray powder diffraction and energy dispersive spectroscopy to assess their compressive strengths and microstructure. The results show that after thermal shock via air-cooling, geopolymer concrete exhibited superior compressive strength and microstructure than conventional concrete. Concurrently, after thermal shock via water-cooling geopolymer concrete retained more of its compressive strength and microstructure than OPC. The findings demonstrate that geopolymer concrete holds an advantage in water and air-cooling based thermal shock situations and thus can be applied in conditions where there is a higher risk of fire that would require immediate quenching with water.

Flexural Behavior of Carbon Textile-Reinforced Geopolymer Composite Thin Plate

Textile-reinforced Portland cement-based concrete has been researched and developed over the last few decades. It was widely used in a different range of applications, such as repair and/or strengthening of structural elements, thin walls, lightweight structures, façade elements, and others. Due to its varied application, this study aims to develop the carbon textile-reinforced geopolymer composite. Specimens of rectangular form with the dimensions of 400 × 100 × 15 mm3, reinforced with carbon textile, were produced. Four-point bending test was used to evaluate the effect of carbon textile on the mechanical strength of reinforced geopolymer composite based on the three factors: the different mortar compositions corresponding to the addition of the chopped basalt fiber (BF), the number of carbon textile layers, and the different thicknesses of the mortar cover layer. Besides that, a small part of the pull-out test was also considered to assess the adhesion strength at the interface between carbon textile and geopolymer mortar. The experimental results from the four-point bending test showed that the mechanical strength of composite specimens increased when the content of the chopped basalt fiber increased. With the increasing number of the textile layers, the specimens improved the flexural strength significantly. However, the flexural toughness of the specimens reinforced with three textile layers did not improve, as compared to those reinforced with two textile layers. The experimental results for the specimens related to the mortar cover thicknesses indicated that specimens with the mortar cover thickness of 2 mm provide the best strength. The experimental results from the pull-out tests showed that all the specimens have the same failure mode by slipping of the fiber yarn from the matrix.

Sustainable concrete construction – from recycled demolition aggregate to alkali activated binders

Investigations into the economics, practicalities and technicalities of using recycled demolition aggregate in concrete precast products started in 2001. At that time, there were six demolition contractors around Liverpool and they were using mobile crushers which were suited for road subbase material but not for the smaller sized aggregate required for precast concrete products. It was estimated that if all six worked round the clock, i.e. assuming there was enough feed material, they would still have found it difficult to maintain the required supplies for a single precast factory. Investment in equipment was therefore required to guarantee supply and improve the quality of the recycled demolition aggregate. The market forces and the incentives/drivers for construction companies to adopt sustainable practises have encouraged investment of several million pounds to be made in new recycling plants and this has resulted in “urban quarries”.Work on reducing the carbon footprint of concrete construction needs to consider not only the replacement of the aggregate with recycled ones but also to consider a reduction or complete replacement of Portland cement in concrete mixes. Alkali activated binders and geopolymers have seen applications in ceramics, hazardous waste containment, fire-resistant construction materials and refractories but the most interesting application is their use to replace Portland cement-based concretes. Several factors affecting the reactivity of fly ash as a precursor for geopolymer concrete have been investigated. These include physical and chemical properties of various fly ash sources, inclusion of ground granulated blast furnace slag (ggbs), chemical activator dosages and curing temperature. Alkali-activated fly ash was found to require elevated curing temperatures and high alkali concentrations. A mixture of sodium hydroxide and sodium silicate was used and this was shown to result in high strengths, as high as 70 MPa at 28 days. The partial replacement of fly ash with ground granulated blast furnace slag (ggbs) was found to be beneficial in not only avoiding the need for elevated curing temperatures but also in improving compressive strengths. It became apparent that the main obstacle to commercialisation of these new alternative binders was the cost of the activating solutions, i.e. the sodium hydroxide and the sodium silicate. The latter is the most expensive one and results in geopolymer concretes that cannot compete on price with Portland cement concretes. Attempts therefore concentrated on developing a procedure for the production of sodium hydroxide from waste streams, which in this case was ground glass cullet. Production of eco-friendly concretes thus becomes commercially possible.

Alkali-silica reaction in waterglass-activated slag mortars incorporating fly ash and metakaolin

Mitigation of alkali-silica reaction (ASR) in concrete is essential for durable and sustainable constructions. In conventional Portland cement-based concrete, alumina-rich supplementary cementitious materials such as low-calcium fly ash and metakaolin have been successfully used to mitigate ASR. Such effect has not been investigated for alkali-activated slag based materials. In this study, ASR expansion, changes in mortar weight and pore solution alkalinity have been studied. XRD and SEM/EDX have been employed to examine the reaction products and degradation of aggregates. The results demonstrate that there is an optimum dosage of fly ash to reduce ASR expansion of the studied mortars, whereas ASR expansion decreases with increasing the amount of metakaolin. It is found that the amount of ASR product formed is minor in the studied mortars with highest expansion. The pore solution alkalinity of the studied mortars is the main factor which controls the ASR in the alkali-activated slag mortars.

Low dosage nano-silica modification on lightweight aggregate concrete

Although the nano modification has been considered as a promising approach to enhance the mechanical properties of cement-based concrete, the investigation of low dosage nano modification on lightweight cement-based concrete is still very limited. In this study, the lightweight concrete, which was modified with low dosage nano-silica particles, were investigated. Non-prewetting and prewetting methods were used to prepare the lightweight concrete samples. The compressive and flexural strengths were tested to evaluate the modification effects of low dosage nano-silica on lightweight concrete. The microstructure analyses demonstrate that the hydration process of the cement paste can be changed with addition of nano-silica, and new types of hydration products have been observed in nano modified cementitious matrix. The interface between the lightweight aggregates and the cement paste can be reinforced by low dosage of nano-silica due to the new types of hydration products. However, relatively high dosage of nano-silica will reduce the modification effect because of the internal stress, which is resulted from the volume expansion of the new types of hydration product, at the interface of the lightweight aggregates and the cement paste. This study not only shows the possibility of low dosage nano modification on the mechanical properties enhancement of lightweight concrete but also provides potential modification mechanisms, which help to design and fabricate high-performance lightweight concrete materials.

二灰稳定碎石再生水泥混凝土基层材料的性能研究

二灰稳定碎石再生水泥混凝土基层材料的性能研究

Numerical simulation of low temperature on plastic runway of cement base

Surface polyurethane materials in sports venues, which have good elasticity, high strength, excellent wear resistance and fine damping capacity, easily crack in winter. These cracks will affect their service performance for applications in sports. In this study, the temperature and stress distribution in cement concrete base layers in sports venues was investigated. A transient, two-dimensional finite-element model was built to predict the transient temperature distributions at various depths in a plastic runway of cement concrete base using the Ansys software. The results show that the temperature change almost occurs in the surface polyurethane layer. The low thermal conductivity of the polyurethane layer will be helpful for temperature distribution across the layer in winter. It should be realized to control or decrease the crack’s appearance in the plastic runway. Ultimately, the model is aimed at providing runway engineers with an efficient computational tool that attempts to increase the prediction accuracy of temperature in plastic runways of cement concrete base layer in cold regions for more reliable runway design.

Towards poured earth construction mimicking cement solidification: demonstration of feasibility via a biosourced polymer

The feasibility of building with earth in the same and simple way as cement-based concrete has been demonstrated as an environmental-friendly alternative. Sodium alginate, a bio-sourced polymer, is used to induce a liquid–solid transition to a clay based suspension, similar to hydraulic binders. The polymer gelation occurs via calcium ions released from the binding phase through a gentle acidification of the mix. It leads to a substantial solidification of the wet material, theoretically sufficient to remove the formwork of an earth wall within 24 h without waiting for drying. Working time is adjusted using a chelator which forms complexes with calcium ions.