Effect Of Different Admixtures Research Articles

Improvement of subgrade California Bearing Ratio (CBR) using recycled concrete aggregate and fly ash

The study aims to understand the effect of different admixtures on improving the quality of flexible pavement subgrades. In this paper, recycled concrete aggregates (RCA) and Fly Ash were used as the admixtures in improving the maximum dry density (MDD), swelling potential, and California bearing ratio (CBR) of subgrade soil. The percentages of RCA and fly Ash used were 5%, 10%, and 15%. With the upscaling in fly ash dosage, the optimum moisture content and the California bearing ratio increased. However, the MDD of soil decreased for higher fly ash contents. On the contrary, the optimum moisture content (OMC) of the soil decreased and the MDD and California Bearing Ratio increased with an increase in RCA content. Both RCA and fly ash-treated soil demonstrated lower values of swelling. At 5% dosage, both RCA and fly ash admixtures were found to improve CBR. However, at higher percentages (10% and 15%) of fly ash, the CBR values decreased while in comparison, soil samples performed significantly better in the CBR test with the increasing dosage of RCA. The findings of this research can be used to examine the suitability and effects of recycled aggregate and fly ash on the performance of soil in terms of CBR, particularly when the soil is planned to be used as a subgrade in highways.

Hydration mechanism of calcium chloride modified coal gasification slag-based backfill materials

To address the environmental pollution and resource wastage caused by the massive stockpiling of coal gasification slag (CGS), in this study, chlorine salt (CaCl2, CC) was adopted to stimulate the potential volcanic ash activity of CGS and to prepare a new modified CGS-based cementitious backfill material (MC-CPB). The optimum CC admixture was determined by comparing the compressive strength, and the effect of different admixtures on the strength of the MC-CPB was investigated. The effects of the CC content on the hydration properties and the composition and the micro-morphology of the hydration products of the MC-CPB were analyzed using hydration heat, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetry (TG) analyses. It was found that the addition of CC promoted the early and mid-strength of the MC-CPB, but an excessive amount of CC (>1%) inhibited the development of the strength in the later stages. A concentration of 1% CC had the best effect on the strength of the MC-CPB in the entire age range, increasing the compressive strength from 3 to 90 days by 65.8%, 56.1%, 80.6%, 30.9%, and 31% compared to the control group. The CC accelerated the hydration reaction process of the MC-CPB by shortening the durations of the induction and acceleration periods, and it enhanced the hydration reaction intensity of the MC-CPB by increasing the second release heat peak and forming a third release heat peak. The MC-CPB sample containing CC generated a new hydration product, Friedel’s salt, which increased the compactness of the matrix and thus improved the compressive strength of the sample. However, excessive addition of CC reduced the amount of Ettringite (AFt) generated in the later stage, leading to a decrease in the strength of the high CC content samples in the later stage. The results of this study promote the large-scale and resourceful use of CGS in mine backfill and provide a theoretical basis for the field proportioning design and industrial application of MC-CPB for backfill.

Optimization of the Grout Mix Ratio and Simulation Test of Shield Tail Grouting Similarities in a Water-Rich Fine Sand Layer

When shield tunneling is performed in water-rich silt and fine sand strata, the grout becomes runny when diluted by groundwater. After dilution, the filling effect of the grout is not significant, and the level of surface settlement is very high. In this study, based on bidding section 04 of Tianjin Metro Line 11, traditional grouting materials were selected to conduct response surface method (RSM) tests. The purposes of the RSM analysis were to analyze the interactions between materials and their influences on grout performance and to optimize the grout mix ratio. Various admixtures were compared to assess the effects of different admixtures and compositions on the dispersion resistance and flow performance of the grout. Finally, a shield synchronous grouting test system was developed, and a similar indoor grouting simulation test was performed to analyze the influences of the different admixtures on the filling effects and to determine a reasonable grout mix ratio. The following three results were obtained. (1) The RSM was suitable for grout performance prediction and grout mix ratio optimization, and hydroxyethyl cellulose could improve the grout performance and increase the bond performance between the cementing material and aggregate. (2) Admixture incorporation enhancement could improve the grout utilization rate and increase the diffusion distance at the top of the tunnel, which would be conducive to filling the gap at the tail end of the shield. (3) The optimal preparation scheme of grout in water-rich fine sand formations included a water–binder ratio of 0.72, cement–sand ratio of 0.80, fly ash content of 5%, bentonite content of 14.94%, and admixture content of 0.8%–0.9%

Comparative Study on the Effect of Different Admixtures in Concrete

Abstract: Concrete is one of the most widely used construction material across the world. It is a composite material composed of aggregate bonded together with fluid cement that cures over time. Various types of admixtures are added to concrete mixtures in order to reduce the cost of concrete construction; to modify the properties of hardened concrete; to ensure the quality of concrete during mixing, transporting, placing, and curing; and to overcome certain emergencies during concrete operations. In this study, an attempt has been made to obtain the better type of concrete sample by adding different types of admixtures. Concrete samples are prepared by using two types of admixture i.e. chemical and economical admixtures. Slump test was performed in fresh concrete samples and Compressive strength test has been conducted for the hardened concrete samples with both chemical and economical admixture after 7 days and 28 days.

Effects of Different Admixtures on the Mechanical and Thermal Insulation Properties of Desulfurization Gypsum-Based Composites

The single-factor experiments are designed to quantitatively investigate the effects of silica fume, mineral powder, and fly ash on the mechanical and thermal insulation properties of desulfurization gypsum-based composites (DGCs). The effect mechanism is discussed from the microscopic morphology of the internal structure, and the corresponding relationship between the strength and thermal conductivity of this material is evaluated by the regression model. The results show that the admixture of silica fume, mineral powder, and fly ash improves the strengths and thermal insulation properties of DGCs, with the order of influence silica fume > mineral powder > fly ash. The optimal 28 d compressive strength and thermal conductivity are 34.17 MPa and 0.2146 W/(m·K), respectively, at a silica fume dosage of 35%. The enhancement effects on the strength and thermal insulation performance of DGCs are attributed to the increase in the hydration products C-S-H gel and Aft. Moreover, the thermal conductivity linearly decreases with the increase in the compressive strength of DGC after adding silica fume, mineral powder, and fly ash. The linear regression models exhibit good precision for evaluating the corresponding relationships between the compressive strength and thermal conductivity of DGCs with different admixtures.

Study on the effect of plant extracts as low carbon green admixtures on the performance of cement mortar

The pollution of the environment by chemical admixtures for cement and concrete and the carbon emission in the production of cement and other concrete raw materials have attracted increasing attention from scholars. In order to improve the physical and mechanical properties of cement, eliminate pollution and reduce carbon emission, this paper uses natural plant extracts (cactus sativus extract and mulberry leaf extract) as admixtures to make cement mortar. The consistency, water absorption, compressive strength, flexural strength, chloride ion penetration resistance and microstructure of the mortar were tested and analyzed, the effects of different admixtures of natural plant extracts on the physical and mechanical properties of cement mortar were investigated. The results show that the consistency of the cement mortar was increasing with the increase of the admixture of cactus sativus extract and mulberry leaf extract; the admixture of cactus sativus extract and mulberry leaf extract did not change the hydration reaction and hydration products. When the admixture amount was lower, the extracts could promote the hydration reaction, improve the internal crystal morphology and generate more C-S-H, thus improving the physical and mechanical properties of cement mortar. The physical and mechanical properties of the cement mortar were optimized when the amount of mulberry leaf extract was 0.15% of the cement mass, and the overall performance was improved more compared with that of cactus extract. With the increase of amount of admixture, the viscosity of the system increases due to plant extracts, and the air bubbles formed during mortar mixing cannot be discharged and form micro-pores inside, resulting in the reduction of physical and mechanical properties. As a low carbon green admixture, plant extract is worthy of further research and promotion.

Effect of Admixtures on Selected Properties of Fly Ash-Based Geopolymer Composites

This research was carried out to expand our knowledge of the effects of different admixtures on the properties of fly ash-based geopolymer composites. Three admixtures were used: a liquifying admixture based on stabilized polycarboxylates, a plasticizing admixture, and a liquifying admixture based on modified polynaphthalenes. The effect of variable activator content relative to the binder was also tested. The most favorable flexural and compressive strengths as well as water absorption were obtained in the series with a liquifying admixture based on stabilized polycarboxylates and an activator to fly ash ratio of 0.5 or 0.6. An increase in flexural and compressive strengths of 11% and 32%, respectively, was obtained compared to the series without admixtures. No positive effect was found for plasticizing admixtures or those based on modified polynaphthalenes.

Development of a high strength cementitious grout for filling the joints of UHPC permanent formwork

The utilization of ultra-high-performance concrete (UHPC) permanent formwork could facilitate the construction of hydraulic concrete structures. However, the joints between UHPC formwork are the vulnerable parts of a whole permanent formwork system. This study aimed to develop a High Strength Cementitious Grout (HSCG) for filling these joints, integrating the formwork system, and minimizing the adverse influence on these joints. The aggregate size for the HSCG was optimized, and four kinds of admixtures (i.e., hydrophobic powder (HP), expansive agent (EA), redispersible polymer powder (RPP), and cellulose ether (CE)) and PVA fibers were used to improve the HSCG. The HSCG with different aggregate sizes, admixture dosages, and PVA fiber contents were experimentally investigated. By evaluating the compressive, tensile, flexural, and adhesive strengths of the prepared grout, the aggregate size range was recommended to be 0.15–0.30 ​mm, while the suggested contents of HP, EA, RPP, and CE were 0%, 6%, 2%, and 0.1%, respectively, by weight of binding materials. In addition, the optimal volume content of PVA fibers was 0.45%. In order to avoid the introduced foams, 0.2% of the defoamers were used in combination with the CE. After that, six combinations were tested to consider the coupled effect of different admixtures and PVA fibers on the HSCG. In consideration of the strengths, shrinkage, and abrasion resistance to water impact, the HSCG with the combination of (EA ​+ ​RPP ​+ ​CE), the aggregate size of 0.15–0.30 ​mm showed the optimal overall performance and was regarded as the most suitable HSCG for grouting.

Effect of Different Admixtures on Pore Characteristics, Permeability, Strength, and Anti-Stripping Property of Porous Concrete

To solve the problem of insufficient strength and durability of porous concrete pavement, seven different admixtures were used in this study so that the above properties could be optimized. The strengthening effect of admixtures on the strength and anti-stripping property of porous concrete was evaluated. The effects of different admixtures on the pore characteristics, strength, and anti-stripping of porous concrete were analyzed with CT tomography technology. The relationship between the pore characteristics of porous concrete and its strength, the anti-stripping property, was explored separately, and the correlation between the strength and anti-stripping property was also investigated. The addition of admixtures affected the pore characteristics of porous concrete, and there was no significant correlation between them. The strength of porous concrete was improved by the addition of admixtures, but the addition of different admixtures had different effects on the improvement of strength. Meanwhile, there was no significant correlation between the strength and pore characteristics. Adding admixtures could improve the anti-stripping property of porous concrete, however, different admixtures had different improvement effects. The effect of porosity on anti-stripping property was limited, while the pore number and equivalent aperture had no effect. There was no obvious correlation between the strength and anti-stripping property of porous concrete prepared with different admixtures.

3D-printable quaternary cementitious materials towards sustainable development: Mixture design and mechanical properties

Development of 3D-printing technologies for cementitious materials becomes one of the driving forces to accelerate innovation in modern construction. The use of mineral and chemical admixtures in concrete has been found to benefit fresh and hardened properties and reduce the carbon footprint of portland cement. Towards this aim, four different supplementary cementitious materials, including metakaolin, silica fume, blast furnace slag, and sodium metasilicate, were utilized in binary, ternary, and quaternary cementitious blends. Flowability, setting, and compressive strength were measured to investigate the effects of different admixtures and their combinations on materials properties of printable mixtures. Selected mixtures were 3D-printed into cylinder specimens to assess their printing quality. The optimal mixture with up to 32.5% cement replacement was 3D-printed to evaluate mechanical properties (i.e., compressive strength and elastic modulus) based on prism specimens. The anisotropic behavior under compression load was observed. 3D-printed specimens tested under perpendicular direction showed the lowest compressive strength but the highest elastic modulus.

Comparative Study on the Effects of Various Modified Admixtures on the Mechanical Properties of Styrene-Acrylic Emulsion-Based Cement Composite Materials.

This study carried out tensile tests at definite elongation, tensile and shear tests on 4 admixture-modified styrene-acrylic emulsion-based cement composites (SECCs), and measured the strength, deformation, and energy consumption indexes of test specimens, so as to investigate the influences of coalescing agent, plasticizer, silane coupling agent, and nanometer aluminium oxide on the bond, tensile, and shear mechanical properties of the test specimens. Additionally, the Field Emission Scanning Electron Microscope (FE-SEM) test and Mercury Intrusion Porosimetry (MIP) test were conducted on the composite material specimens, to analyze the microscopic mechanism of different admixtures in modifying the mechanical properties of the SECC. The results suggested that the addition of coalescing agent, plasticizer, silane coupling agent, and nanometer aluminium oxide improved the bond, tensile and shear properties of the SECC specimens to various degrees. Of them, the coalescing agent promoted the mutual cross-linking of organic polymers with inorganic products, and optimized the transition interface to enhance the comprehensive mechanical properties of the test specimens; by contrast, nanometer aluminium oxide developed secondary hydration reaction with the inorganic products, and refined the pore structure to modify the mechanical properties of test specimens. Therefore, both of them achieved significant modification effects. Typically, the optimal bond properties of FFAMC, PLMC, SCAMC, and NAMC test specimens were achieved at the coalescing agent, plasticizer, silane coupling agent, and nanometer aluminium oxide addition amounts of 4%, 1.5%, 3%, and 1%, respectively. Besides, the improving effects of different admixtures on the tensile property of SECC specimens followed the order of coalescing agent > nanometer aluminium oxide > plasticizer > silane coupling agent, with the optimal addition amounts of 4%, 1.5%, 1%, and 2%, respectively. In addition, the improving effects of different admixtures on the shear performance of SECC specimens followed the order of coalescing agent > nanometer aluminium oxide > silane coupling agent > plasticizer, with the optimal addition amounts of 4%, 1.5%, 1%, and 1%, respectively.

Effect of Different Additives Addition on Basic Magnesium Sulfate Cement Composite Sheet

Study the effects of different admixtures and different dosages on Basic Magnesium Sulfate Cement (BMS) composite sheets, the effects of sodium citrate and phosphoric acid on the flexural strength and compressive strength of basic magnesium sulfate cement sheets were studied, XRD and SEM were used to analyze the composition and microstructure of hydration products. The results show, the addition of admixtures has a great influence on the properties of composite sheets. Adding the corresponding proportion of admixture to the plate, the mechanical properties are significantly improved. Therefore, the properties of sheet metal can be greatly improved by choosing appropriate additives.

Strength and Porosity of Materials on the Basis of Blast Furnace Slag Activated by Liquid Sodium Silicate

This study investigates the effect of different admixtures on strength and porosity development of mortars and pastes based on alkali activated blast furnace slag (AABFS). Fluidized bed combustion fly ash and by-pass cement kiln dust were used to replace slag in the binder by 5%wt. and 10%wt., respectively. Pure slag mortar was also modified by a shrinkage reducing admixture. The use of all the admixtures resulted in a reduction in early age strength, while only shrinkage reducing admixture had significant impact on pore size distribution. Properties of AABFS based specimens were compared to those of specimens based on ordinary Portland cement (OPC).

Improving Pervious Concrete Pavements for Achieving More Sustainable Urban Roads

Pervious concrete is a novel pavement material characterized by a porous structure that allows the water to percolate through it with consequent numerous environmental benefits. However, high-drainability characteristics do not generally correspond to high strength and good surface conditions when submitted to vehicular traffic, hence, to date, the applications of pervious concrete are limited to particular urban areas. In addition, mix design and rigorous construction standards have not yet been defined. The present laboratory study aimed to compare the properties of several pervious concrete mixtures submitted to different compaction energies. The main objectives were, on one hand, to define the effects of compaction energy on the design requirements of strength and drainability, on the other, to compare the reinforcing effect of different admixtures on the material properties. Different percentages of sand and several reinforcing fibres with various physical and chemical properties were added to the mixes, changing water to cement ratio while fixing the aggregate size distribution and the paste content. Laboratory tests, such as indirect tensile strength, elastic modulus, and Cantabro resistance, were conducted to measure the mechanical behaviour of the material; while, porosity, bulk density and drainability capacity were evaluated to define volumetric and functional characteristics. The result of this investigation provided useful information about the effectiveness of laboratory compaction to achieve the optimal strength-drainability balance, adequate for the different urban uses. Moreover, this study identified the suitable admixtures, with the appropriate proportioning, that could enhance the mechanical properties of the material leading to a wiser use in medium-high traffic roads.

An experimental study on earth plasters for earthen building protection: The effects of different admixtures and surface treatments

Abstract In rainy climates, the external surfaces of earthen buildings suffer water erosion. In this paper, the properties of earth plasters have been investigated considering the specific relationship with the underlying substrate. Ten typologies of earth plasters containing different admixtures and surface treatments, a cob wall and a rammed earth wall were produced in laboratory. The aim is to evaluate the effectiveness of the coatings in protecting the earthen walls against weathering. An in situ procedure consisting of a shrinkage test followed by an adhesion strength test was performed in order to identify the earth/sand ratio optimal for the plaster manufacturing. Then, a series of tests was carried out both on the plasters and the two walls: compression, water vapor permeability, surface color, wettability, water absorption and erosion. The results demonstrate that all the plasters are physically and mechanically compatible with the earthen substrates and that the most important differences are in the specific relationship with water. The earth plaster treated with the silane–siloxane product was found to be the best one: it is fully compatible, water-repellent and highly resistant to water erosion. Hence, there is a potential for the use of earth plasters for the protection of earthen buildings against weathering.

CONTRIBUTION TO THE DESIGN OF HYDRAULIC LIME-BASED GROUTS FOR MASONRY CONSOLIDATION

Grout is a concentrated suspension that can be employed for the homogenisation and consolidation of systems presenting pores, voids and cracks, such as inner core of old stone masonries. A grout should be well conceived, taking into account the optimisation of its performance; this means that simple binder and water formulations prove to be inadequate. Hence, the effect of different admixtures and pozzolans, which are traditionally used in concrete, on the fresh and hardened properties of hydraulic lime grouts, were investigated. Hydraulic lime binder plays a role of great importance in the rehabilitation of historic structures, due to its compatibility with pre-existing materials, like mortars. However, hardly any information is presently known regarding the effect of these materials on the behaviour of hydraulic lime grouts. The improvement of their properties through the use of these products is still an open field. Hence, and as a first step, the prediction of grout properties in a laboratory setting were made. The results summarised in this paper are part of a large research project and precede the fine tuning of grout composition according to the characteristics of the masonry to which such a grout is to be injected.

Study on the Effect of Different Admixtures on the Early Autogenous Shrinkage of High Performance Concrete of Bridge Deck Pavement

This paper analyzed the mechanism of early autogenous shrinkage of concrete, and studied the influence of early autogenous shrinkage of high performance concrete-(HPC) admixed with different kinds of materials of bridge deck pavement. Four different concrete mixes were used: fiber, fiber plus expansive agent, fiber plus fly ash and fiber plus shrinkage-reducing agent. The result shows that the four different mixes can inhibit the autogenous shrinkage of HPC to a certain extent, the inhibitory effect of different mixes in the order of strong to weak is: fiber plus shrinkage-reducing agent, fiber plus fly ash, fiber plus expansive agent, and fiber itself. Furthermore, the inhibition mechanism of each mix was analyzed and a conclusion of mixture of fiber plus fly ash to be the best choice considered of economic and working performance is drawn as well.

Studies on Effect of Refractory Chemicals on Cement Mortar

Concrete has remarkable fire resistance properties. In the case of fire, it is found that the concrete affected by fire depends to a great extent on the intensity and duration of fire. Previous experience has shown that concrete structures are likely to have a good fire rating than structures made of other materials. Nevertheless, concrete undergoes important chemical and physical changes, starting at 400°C - 500°C. As calcium hydroxide and other hydration products start to decompose, concrete tends to lose its strength, typically around 600°C - 700°C. In order to improve the high temperature properties of concrete, admixtures can be used in concrete. In the following, a study on the effects of different admixtures on the properties of concrete at high temperature is presented.

Soil amendments for plantings of urban trees

The effect of different admixtures of gravel to soil on freshly planted urban trees ( Acer platanoides L., Tilia europaea L., T. × euchlora K. Koch, Tilia × europaea L. var. pallida and Platanus × acerifolia (Ait.) Willd.) was investigated. Expanded clay proved to be most favourable for Tilia. It improved soil water regime and aeration. Lava rock was deleterious for Tilia but not for Acer. The effect on trees was not much different in the case of vertical gradients of the admixture compared to homogeneous mixtures. A horizontal gradient with river gravel resulted in a slight stimulation of root development in all species examined in the third year after planting.

Experimental study on the basic phenomena of shrinkage and cracking of fresh mortar

Evaporation, horizontal shrinkage, settlement, setting and capillary pressure of mortar mixes were measured during first hours with samples which were exposured to wind (velocity 4 m/s, T = 20 °C and RH 40%). The effects of different admixtures (super plasticizer, accelerating, retarding, air-entraining agent and one type of fibre) on the shrinking behaviour of the mortars were studied accordingly. The well-known fact that proper long-term wet curing is vital for the crack-free surfaces of concrete or mortar was confirmed experimentally. The beginning of setting can be regarded as a critical moment. After that the mortar has capacity to resist the capillary forces and thus shrinkage. The mix modified by super plasticizer behaved unexpectedly, and the surface of the sample cracked. This cracking was indicated by zig-zag behaviour in the measured horizontal shrinkage and capillary pressure. Air- entraining agent reduced horizontal shrinkage considerably. Use of fibre reduced shrinkage about 30% when compared to mix without fibre. Based on the results some conclusions are drawn concerning properly limed trowelling on horizontal shrinkage.