Addition Of Mineral Admixtures Research Articles

Study on the effect of mineral admixture on the water stability of UHPC under long-term immersion

Ultra-high performance concrete (UHPC) is prone to re-hydration as well as generating new hydration products in high humidity environments, which causes internal expansion and surface cracking. The addition of mineral admixture has a positive effect on long-term water stability of UHPC. In this study, four groups of UHPC specimens with different mineral admixture contents were prepared. Long-term immersion experiments of up to 360 days were conducted. The physical and mechanical properties of those specimens were investigated, and the re-hydration mechanism was revealed by NMR, XRD, and SEM tests. The specimens blended with silica fume and fly ash showed the best water stability, which exhibited the best physical and mechanical properties, and the less water absorption under long-term room temperature immersion. Compared with reference specimen of pure cement, the flexural strength, compressive strength of blended specimens was increased by 12%, 3.6%, and the mass change rate was reduced by 0.95%, respectively. In the early stage of immersion, the gel pore water and capillary pore water in the interior of the specimens were consumed and converted into free water. After 180 d, the percentage of water molecules with strong free degree was increased and the free water molecules were gradually reduced. The mechanism is that the small particle size of the silica fume and fly ash makes the UHPC stacking more compact. In addition, those mineral admixtures have higher volcanic ash effect, which can react with calcium hydroxide in hydration products to generate C-S-H and resulting in denser of UHPC internal structural. The double effect of filling effect and volcanic ash effect prevents more water from entering, which makes UHPC blended with silica fume and fly ash have better water stability.

Effects of Mineral Admixtures on the Evolution of Static Yield Stress of Different Composite Pastes

The effects of different mineral admixtures on the evolution of static yield stress of common composite cementitious material paste and ultra-high-performance concrete (UHPC)-based paste were investigated. The results show that there are obvious differences in the role of mineral admixtures in the common paste and the UHPC-based paste. Adding mineral admixtures can change the initial static yield stress of the paste by affecting the particle size, particle shape and the charged particles. The addition of mineral admixtures with small particle size such as silica fume and ultrafine slag can increase the initial static yield stress of common paste but reduce that of UHPC-based paste. Adding mineral admixtures changes the evolution of static yield stress of the paste by affecting the particle spacing and the formation and growth rate of hydration products. In turn, the addition of ultrafine slag or silica fume increases the growth of the static yield stress of common paste. Adding slag, fly ash or fly ash microbeads successively reduces the static yield stress of common paste at the later stage. Affected by the content of PCE, the static yield stress of UHPC-based paste containing fly ash microbeads, slag, ultrafine slag and fly ash increases sequentially compared with the blank group at the later stage. The effect of silica fume with different dosages on the evolution of static yield stress of UHPC-based paste is significantly different.

A Review of Durability Issues of Reinforced Concrete Structures Due to Coastal Soda Residue Soil in China

Soda residue soil (SRS) is a man-made engineering foundation soil formed by soda residue; it is mainly distributed in coastal areas in China. SRS is rich in a variety of corrosive salts, among which the concentrations of chloride ions are about 2–3 times that of seawater. These highly concentrated chloride ions migrate and diffuse in reinforced concrete (RC) structures built on coastal SRS through multiple transport mechanisms. However, current research on the durability of RC structures exposed to the coastal SRS environment has not led to the publication of any reports in the literature. SRS may be classified by analyzing the quantitative relationships among the corrosive ions it contains. In this paper, the deterioration of RC structures due to the corrosive saline-soil environment in China is discussed, and advances in RC structure durability under such circumstances are reviewed. Our findings show that a corrosive environment, especially when this is a result of coastal SRS, has a significant influence on the deterioration of RC structures, greatly threatening such buildings. A series of effective measures for enhancing the durability of RC structures in saline soil, including improvements in concrete strength, reductions in the water–binder ratio, the addition of mineral admixtures and fiber-reinforcing agents, etc., could provide a vital foundation for enhancing the durability of RC structures which are at risk due to coastal SRS. Vital issues that must be investigated regarding the durability of RC structures are proposed, including the transport mechanism and a prediction model of corrosive ions, dominated by chloride ions (Cl−), in SRS and RC structures, the deterioration mechanism of RC materials, a long-term performance deduction process of RC components, durability design theory, and effective performance enhancement measures. The findings of this paper provide some clear exploration directions for the development of basic theories regarding RC structure durability in coastal SRS environments and go some way to making up for the research gap regarding RC structure durability under corrosive soil environments.

Effects of Mineral Admixtures on Macrocell Corrosion Behaviors of Steel Bars in Chloride-Contaminated Concrete

Based on the macrocell corrosion theory and by alternating the microcell corrosion state and macrocell corrosion state, the influence of mineral admixtures, such as fly ash, slag, and limestone powder, on the macrocell corrosion behaviors of steel bars embedded in chloride-contaminated concrete were investigated and clarified. The results indicated that the inhibition effect induced by slag on macrocell corrosion and microcell corrosion was obviously better than that induced by fly ash or limestone powder. The presence of slag in chloride-contaminated concrete could remarkably decrease the corrosion area ratios of anodic steel, even if the replacement levels of slag to cement reached 70%. With the addition of mineral admixtures into concrete, the ratio of macrocell current density to microcell current density was decreased to some extent, depending on the types, replacement levels, and replacement ways of mineral admixtures. The use of slag and fly ash in chloride-contaminated concrete can effectively weaken the macrocell corrosion and make the corrosion be dominated by microcell corrosion. The types and replacement levels of mineral admixtures also had a remarkable influence on the control mode of macrocell corrosion. The use of slag was more effective than that of fly ash or limestone to weaken the cathode control mode of macrocell corrosion and made the control mode of macrocell corrosion be dominated by jointed control.

Effects of curing regimes on the chloride binding capacity of cementitious materials

Chloride ions play obvious adverse roles in the corrosion of reinforcing steel of concrete structure, which affects the durability and service life of reinforced concrete structure. The durability of hydrothermal cured precast concrete elements is usually lower than that of cast-in-situ concrete structures with the same strength grade, and therefore the chloride ion corrosion of precast concrete should be paid more attention. The chloride binding capacity of cement-based material with different curing regimes was investigated by SEM, XRD, solution titration, and Low-Field NMR. Results show that the curing regime has a significant effect on the microscopic morphology and structure of the hydration products, and consequently affect their ability to bind chloride ions. Under steam curing, the HO-AFm’s transformation had an effect on its chemical binding capacity, while the transformation of C-S-H gels into cellular network structure enhanced the physical adsorption capacity. Autoclave curing leads to the reduction of AFm and the conversion of C-S-H to tobermorite, which reduces the binding capacity of the sample to chloride ions. Furthermore, the addition of mineral admixtures containing more reactive Al-phase components is helpful to improve the ability of cementitious materials to bind chloride ions. For FA and GGBFS, the Al-phase in GGBFS is more soluble to react with chloride ions, and its binding effect is better than that of FA.

Selecting Environment-Friendly Mineral Admixtures to Improve the Durability of Shotcrete under Sulfate Attack

The main purpose of this study was to explore the deterioration of shotcrete with different liquid accelerators and mineral admixtures under sulfate attack. By measuring the mass loss, compressive strength, and relative dynamic elastic modulus of shotcrete with liquid accelerators and mineral admixtures, the regularity of sulfate resistance of shotcrete was obtained. In addition, visual observation of surface macro-morphology of shotcrete was conducted. Compared with shotcrete with 4.0% AR and 7.0% AS, it was found that the overall surface condition of shotcrete with mineral admixtures was better in the presence of 7.0% AF. Meanwhile, the result of MIP analysis showed that adding 7.0% AF or 10% silica fume was more conducive to shotcrete compactness. Furthermore, the crystal composition and micromorphology of hydration products were analyzed by XRD, TG, and SEM. It was found that the addition of mineral admixtures could improve the sulfate resistance of shotcrete to varying degrees in the presence of different liquid accelerators.

Experimental study of magnesium ammonium phosphate cements modified by fly ash and metakaolin

In order to make anti-corrosion coating for steel structure, the prepared MAPC paste should meet the requirements of spraying process and require high fluidity. The purpose of this paper is to prepare MAPC paste with high fluidity. but too high water-cement ratio will lead to the decrease of strength. In order to solve this problem, mineral admixtures are added to improve the performance of MAPC. The strength, fluidity, volume deformation, hydration temperature, early water stability, microstructure and phase composition of fly ash or metakaolin modified high fluidity MAPC paste were tested and analyzed. The results show that the addition of mineral admixture can effectively improve the performance of high fluidity MAPC paste without decreasing the fluidity of the paste, in which metakaolin can improve the strength of MAPC paste better than fly ash; this is due to the formation of more highly reinforced microstructures and denser interfaces between the metakaolin particles and hydration products in the MAPC paste containing metakaolin. Based on the micro-analysis of XRD, SEM and energy dispersive spectrometer (EDS), the improvement mechanism was discussed.

Research on Curing Water Demand of Cementing Material System Based on Hydration Characteristics.

The performance of cover concrete is acknowledged as a major factor governing the degradation of concrete structures. Curing plays a vital role in the development of concrete durability. The effects of different water-binder ratios and mineral admixtures on the curing water demand of concrete were studied by the surface water absorption test. Combined with the characteristics of the hydration heat and chemically bound water of the composition cementing material system, the law of variation for curing water demand was analyzed. The results show that the addition of mineral admixtures can reduce the early hydration rate and hydration exothermic characteristics, and the hydration degree decreases with the increase of mineral admixtures. Due to the filling effect and active effect, the addition of fly ash (FA) and ground granulated blast slag (GGBS) reduces the curing water demand. The curing water demand of cover concrete decreases with the increase of mineral admixture content, and the curing water demand of pure water is the maximum and that of mix FA and GGBS is the minimum. Moreover, there is a strong correlation between the cumulative curing water demand and the chemically bound water content, indicating that the power of water migration mainly comes from the hydration activity of the cementing material system. The results provide a theoretical basis for the fine control of a concrete curing system.

Degradation of Shotcrete Materials Subjected to Sulfate and Chloride Attack in Varying Exposure Regimes

Durability of in situ shotcrete under external sulfate attack was investigated, taking into consideration the addition of mineral admixtures, along with the presence of chloride ions. Three water-to-binder ratios (w/b), i.e., 0.35, 0.45, and 0.55, and two types of supplementary cementitious materials (SCMs), namely, fly ash (FA) and silica fume (SF), were considered in the current study. Two different laboratorial immersion regimes (continuously full immersion and partial immersion with cycling temperature and relative humidity) were carried out to induce chemical/physical sulfate attack. Results show that loss of strength was the typical feature of chemical sulfate attack on shotcrete, while surface spalling dominated in deterioration caused by physical sulfate attack. The presence of chloride ions can globally mitigate these deteriorations. Meanwhile, the lower w/b ratio proved to be efficient in increasing the resistance to both sulfate attacks. Adding fly ash (FA) in shotcrete mixtures enhanced the long-term performance but invited massive white efflorescence on surface layer under partial-immersion exposure condition. Silica fume (SF) admixture can compensate the undesired reduction of early-age strength caused by FA addition, but make these specimens more susceptible to sulfate attack. Mercury intrusion porosimetry (MIP) analysis, scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests reveal that these consequences were strongly related to the refinement of microstructure resulted from pozzolanic reactions and hydration kinetics.

Influence of Mineral Additives on the Efflorescence of Ettringite-Rich Systems.

Efflorescence is aesthetically undesirable to all cementitious materials products and mainly results from the carbonation of hydrates and salt precipitation. Alternative binders without portlandite formation theoretically have much lower efflorescence risk, but in practice, the efflorescence of ettringite-rich systems is still serious. This study reports the impacts of mineral additives on the efflorescence of ettringite-rich systems and the corresponding microstructural evolution. The effects of silica fume, limestone powder, and diatomite on efflorescence and the capillary pore structure of mortars were investigated from a multi-scale analysis. The composition and microstructure of efflorescent phases were revealed by optical microscope (O.M.), in-situ Raman spectroscopy, and Scanning Electron Microscopy (SEM). Results indicate that the addition of mineral additives can efficiently inhibit the efflorescence of reference, especially with silica fume. Similar to the ettringite-rich system, the efflorescence substances of all modifies are composed of ettringite and CaCO3, indicating that the addition of mineral admixture does not lead to chemical reactions, lower capillary absorption coefficient of mineral additives modified specimen, the denser pore structure and the lower efflorescence degree.

Effect of temperature curing on lightweight expanded clay aggregate concrete

Lightweight Aggregate Concrete is usually a mix of Lightweight Aggregates and admixtures. This paper is focused on use of Lightweight Expanded Clay Aggregate (LECA) for the development of structural Lightweight Concrete. The present investigation was carried out by replacing LECA with 30% of Normal Weight Aggregate (NWA) with different water to binder (w/b) ratios to produce an M 30 grade Lightweight Expanded Clay Aggregate Concrete i.e. LECAC30 (30% LECA + 70% NWA). LECAC30 was cured with potable water at boiling temperature for different durations like 3hrs, 6hrs and 9hrs and the effect of temperature curing on early development of compressive strength of Lightweight Expanded Clay Aggregate Concrete was studied. The study also includes the improvement of compressive strength of LECAC30 under temperature curing with 10% addition of mineral admixture. The results obtained in this research conclude that, optimum duration for temperature curing at 100°c was obtained as 6 hrs, the addition of mineral admixture to LECAC30 resulted in an improvement of compressive strength and addition of mineral admixture had no significance in early development of compressive strength under temperature curing.

Investigation on Durability Properties of Self Compacting Concrete with Mineral Admixtures

Self-Compacting Concrete (SCC) or Self Consolidating Concrete is the present-day concrete that is being adopted the world over. The production of SCC involves the selection of appropriate materials and good quality control which is essential for the durability of concrete. The mineral admixtures and filler materials provide additional reduction to the porosity of the concrete. The primary objective of the present research work is to carry out the experimental investigations on durability properties of SCC with 20 different mix proportions, containing various percentages of filler materials like Limestone Powder (LP) and Marble Powder (MP), along with the mineral admixtures like Fly ash (F) and Silica Fume (SF). Experimental investigation on the durability properties for all the 20 mixes of SCC was carried out by conducting the Rapid Chloride Penetration Test (RCPT), Saturated Water Absorption Test, Acid Resistance Test, Sulphate Resistance Test, Water Permeability Test and Salt Water Resistance Test. From the experimental study, it is observed that the SCC mix with equal proportions F (10%), SF (10%), LP (10%) and MP (10%), exhibit better performance than the control mix in terms of strength and durability characteristics and thus it is concluded that the addition of mineral admixtures and filler materials have a pivotal role in the development of strength and durability aspects of SCC.

Evaluation of Heat Insulation and Surface Resistivity of Mineral Lightweight Aggregate Concrete(MLAC)

In this study, the fixed water/binder ratio is 0.40, four mineral admixtures: fly ash (FA), blast furnace slag (BFS), desulphurization slag (DLS), and glass LED powder (GLP), were added to lightweight aggregate concrete (LWAC), replacing 10% or 30% of the cement content, to study their heat insulation efficiency and engineering performance and to compare the economic impact of mineral admixtures on LWAC. In terms of heat insulation, the thermal conductivity (K value) of the controlled sample was 0.484 kcal/(m.h. °C) and the addition of mineral admixtures changed the concrete unit weight and water absorption ratio, thus reducing the K value by 0.41% to 25.71% and improving the heat insulation. As the mineral admixture hydration products and chemical contents differed, the heat insulation of the LWAC varied as well. The study indicated that the heat insulation is the greatest in concrete with the addition of 30% FA, followed by concrete with the addition of 10% GLP. The addition of mineral admixtures is 30%, the resistivity is 72–455% of the control group, and the resistivity of FA and GLP is higher than the control group. The study is indicated that the proper addition of mineral powder material has an apparent effect on increasing heat insulation efficiency.

Mechanical properties of rubber aggregates based geopolymer concrete - A review

Aggregates are the furthermost vital components of concrete, but there is a need for replacement of these natural resources due to the insufficient availability of the materials. To overcome the difficulty of materials and to develop sustainable concrete, much research has been conducting to date. The replacement of aggregates wholly or partially is one of the best alternatives to this problem. To develop sustainability in concrete waste materials that are causing depletion to the environment are used as alternative materials. Rubber tire waste is one such material which is causing a lot of greenhouse gas emission. This paper reviews the use of rubber tire waste as aggregates in geopolymer concrete which shows the effect of various sizes of rubber, untreated and treated rubber aggregate on various properties such as Fresh Properties where flow values of mortar reduced with escalation in the rubber and workability of the mortar and concrete increased. Nevertheless, the Mechanical Properties shows a decrement in compressive strength, and tension properties show an increment. There is a significant amount of increment in the possessions of mortar and concrete after the crumbed rubber treated. The loss of strength for the small amount of replacement of rubber, which is 5-10% shows the strength higher than the standard concrete. The outcomes show that the custom of the rubber in concrete primes to a substantial amount of strength loss, but the addition of mineral admixture and superplasticiser helps us to achieve the geopolymer mortar and concrete applications in the field of construction.

Estimating strength properties of geopolymer self-compacting concrete using machine learning techniques

There has been a persistent drive for sustainable development in the concrete industry. While there are series of encouraging experimental research outputs, yet the research field requires a standard framework for the material development. In this study, the strength characteristics of geopolymer self-compacting concrete made by addition of mineral admixtures, have been modelled with both genetic programming (GEP) and the artificial neural networks (ANN) techniques. The study adopts a 12M sodium hydroxide and sodium silicate alkaline solution of ratio to fly ash at 0.33 for geopolymer reaction. In addition to the conventional material (river sand), fly ash was partially replaced with silica fume and granulated blast furnace slag. Various properties of the concrete, filler ability and passing ability of fresh mixtures, and compressive, split-tensile and flexural strength of hardened concrete were determined. The model development involved using raw materials and fresh mix properties as predictors, and strength properties as response. Results shows that the use of the admixtures enhanced both the fresh and hardened properties of the concrete. Both GEP and ANN methods exhibited good prediction of the experimental data, with minimal errors. However, GEP models can be preferred as simple equations are developed from the process, while ANN is only a predictor.

Mitigating inclusion-induced shrinkage cracking in cementitious composites by incorporating recycled concrete fines

Recent studies on utilization of recycled concrete have demonstrated that usually discarded finest fractions can be incorporated into cementitious composites without scarifying their structural performance. It has been shown that these fines can increase the resistance of a cementitious matrix to tensile stresses and reduce shrinkage, and that these effects can be boosted by addition of mineral admixtures. Such findings led us to a consideration that incorporating recycled concrete fines into a concrete mix could possibly mitigate aggregate-induced shrinkage cracking. Here, this hypothesis was put under scrutiny in a comprehensive experimental-numerical study, confirming that blending Portland cement with recycled concrete fines can mitigate inclusion-induced shrinkage cracking, especially when combined with fly ash. The results of coupled hygro-mechanical modeling indicate that incorporating recycled concrete fines leads not only to a decrease of shrinkage but also increases fracture energy and thus has a major impact on the reduction of micro-cracks between inclusions.

Experimental, statistical and simulation analysis on impact of micro steel – Fibres in reinforced SCC containing admixtures

Self-compacting concrete is one of the special concretes that flow in its own weight, which is used in the densely reinforced concrete structures. This concrete requires higher binder content. Higher cement content leads to uneconomical design, higher heat of hydration, higher shrinkage, etc. These factors can be counteracted by addition of mineral admixtures. Hence, Fly ash (30%) and micro silica fume (10%) are mineral admixtures replaced with cement. Concrete is having a poor flexural properties; this can be enhanced by using fibrous materials. Addition of steel fibres improves the strain softening property of composite system. Hence hooked ended micro steel fibres are used in this study. In order, to study the fresh and mechanical properties of SCC, totally eight mix (M1 to M8) designs are developed using Nan Su proposed method of mix design, with varying steel fibres (0.0%, 0.25%, 0.50% and 0.75%) and varying binder content. To evaluate the impact of steel fibres in reinforced concrete; four mixes (C-1 to C-4) of prism dimension 0.1 m × 0.15 m × 1 m were cast with optimized steel fibres and mineral admixtures content and tested using standard UTM. The key properties such as deflection, strain softening and effect of orienting the steel fibres along the direction of flow of concrete were studied. Later the experimental work was virtually modeled and analyzed using ABAQUS. In rheological study, the mix containing mineral admixtures showed better fresh concrete properties. Addition of fibres reduced the flowing ability of SCC. There is no significant change in compression strength due to addition of steel fibres. Flexural strength increased by 63% by addition of 0.75% of steel fibres. The SEM analysis helped to study the hydration process and morphological behaviors in concrete structures. The statistical analysis were carried out and regression equations have been developed for the better understanding in the field of micro steel fibre-reinforced self-compacting concrete containing admixtures. Stress-Strain behavior of mix C3 and C4 is more linear compared to C1 and C2, due to presence of micro steel fibres, which is arrested the development of micro-cracks. C4 shows better strength compared to C3, showing steel fibres are aligned align the direction of flow of concrete in between the reinforced structures. The analyzed theoretical model, developed used ABAQUS showed similar displacement results.

The re-swelling behavior of superabsorbent polymers (SAPs) in hardened cement paste with an artificial crack

Re-swelling capacity is a key factor affecting the contribution of superabsorbent polymers (SAPs) to sealing cracks in concrete. In this paper, a new parameter (η), the ratio between the volume of the crack filled with the expansive SAPs and the volume of dry SAPs, is given to evaluate the re-swelling capacity of a single SAPs particle. Moreover, the influences of paste composition, solution properties, and crack width on the η value are studied by an innovative immersion test. The results show that the swollen volume ratio, the ratio of the swollen volume of SAPs during mixing to their dry volume, decreases with the reduction of the water-to-binder ratio and the addition of mineral admixtures. Furthermore, the swollen volume ratio, the solution properties, and the crack width have significant impacts on the η value. The η value rises with an increase in crack width (0.25–1 mm), revealing the restricting effects of cracks on the re-swelling capacity of SAPs. These results indicate that the paste composition, solution properties, and crack width should be considered when designing the self-sealing concrete containing SAPs.

Effect of the Electric Field on the Distribution Law of Chloride Ions and Microstructure in Concrete with the Addition of Mineral Admixtures.

Migration testing of chloride under an electric field is a fast and effective method to determine the corrosion resistance of reinforced concrete against chloride. In this study, a series of admixture-involved (fly ash and slag) concrete specimens were produced for an accelerating chloride diffusion test in 3% NaCl solution under an electric field and natural chloride diffusion in 165 g/L NaCl solution under immersion conditions. Then, the chloride profile and pore structure of concretes aged 56 and 91 days were compared to investigate the effect of the electric field on chloride diffusion as well as the microstructure of the concrete. The results showed that, under accelerating electric field conditions, the degree to which chloride refined the internal pore structure of the concrete was weaker than that under natural immersion conditions. The applied electric field changed the pore structure inside the concrete, but it had little effect on the distribution of total, free, and bound chlorides and their mutual relationship. In addition, it is necessary to consider that the electric field effect on chloride migration varies with the concrete mix proportions.

Laboratory Investigation on Mechanical Properties of Cementitious Composites with a Low Brittleness

In this study, laboratory tests were conducted to investigate the mechanical behaviors of cement mortars incorporated with different admixtures, such as polypropylene fiber (PP), slag, silica fume and fly ash. Orthogonal tests were designed to evaluate the effects of the admixtures on the brittleness. The flexural strengths and the compressive-flexural ratios were selected to evaluate the brittleness. The optimal proportion can be obtained when PP content was 1.6 kg/m3, and the content of fly ash, slag and silica fume was 10%, 20% and 3% of the cement content respectively. Using the optimal proportion, the 3d flexural strength of cement mortar was 5.65 MPa, which was 19% larger than the specimens without the addition of admixtures; the compressive-flexural ratio was 4.1, which was reduced by 19% in contrast to the control group. The flexural strength at 28d was 9.04 MPa, which was 13% higher than the control group; and the compressive-flexural ratio was 4.21, decreasing 24% compared to the control group. SEM technology was utilized to characterize the evolution of the microstructure induced by the addition of mineral admixtures and PP fiber. Results showed that mineral admixtures made the mortars denser, and the PP fiber formed a cross-linking structure, improving the brittle-resistance. The test results provided some guidance for the mixture design of pavement concrete with a high flexural strength and a low brittleness.