EFFECTS OF ALKALI-ACTIVATED FLY ASH ON MECHANICAL AND VEGETATIVE PROPERTIES OF ECO CONCRETE

Strength behavior analysis of fiber reinforced fly ash concrete

Performance of sustainable concretes containing very high volume Class-F fly ash and ground granulated blast furnace slag

Large-scale construction of marine structures in the coastal and offshore areas of Vietnam requires the development of new compositions of hydrotechnical concrete and innovative technologies for the preparation of concrete mixes, as well as their transportation to the place of placement. A preliminary composition of heavy concrete was determined and its properties were studied. The effect of the water-binder ratio (W/B) and the effect of using the developed complex organo-mineral modifying additive consisting of fly ash (FA) of Vung Ang TPP, microsilica SF-90 (SF90) and polycarboxylate superplasticizer SR 5000F (SP) on the concrete properties. To process the obtained results, the method of mathematical planning of the experiment with the construction of a four-factor plan was used. As a result of the studies conducted, first-order regression equations were obtained depending on the objective functions - the mobility of the concrete mixture on the cone sediment, the compressive strength of concrete and the deformations of concrete on input factors - x1 (W/B), x2 (amount of SP), x3 (amount of FA) and x4 (amount of SF90). From the obtained regression equations, it follows that the water-binder ratio, as well as the content of superplasticizer, fly ash and microsilica in the composition of the additive have a significant impact on the mobility of concrete mixtures. When reducing W/B and the amount of FA, as well as the increase in the amount of SF90 (x4) concrete compressive strength in 28 days also increases. The result of this study showed the relative deformation of concrete also increases with an increase in the content of FA and reducing W/B and the amount of SF90. At the same time, the effect of the water-binder relationship is most pronounced. It can be assumed that, in the composition of the developed modifying additive, the particles FA and SF90 played the role of a kind of “sliding bearings” between the grains of cement, with which you can control the dispersion of cement and finely dispersed mineral grains in the concrete mixture, and hence its mobility and persistence construction sites in the coastal areas of Vietnam. In addition, SF90, containing 91.65% of amorphous silica, binds free calcium hydroxide to less soluble low-basic calcium silicate silicates, compresses the structure of concrete and increases its compressive strength.

Influence of Brazilian fly ash fineness on the cementing efficiency factor, compressive strength and Young's modulus of concrete

This study investigated the influences of water-to-binder mass ratio (0.44, 0.47, and 0.50), and waterglass (8%, 12% and 16%) and fly ash (0%, 25% and 50%) contents on the slump, cubic compressive strength, and static and dynamic compressive behaviors of slag-based geopolymer concrete (GC). Static compressive tests were carried out by using an electro-hydraulic servo-controlled compressive test system, and dynamic ones were performed by using a split Hopkinson pressure bar (SHPB) apparatus. The specimens with a wide range of the compressive strength (from 50 MPa to 80 MPa) were prepared. The results show that the workability of fresh slag-based GC increased with increasing water-to-binder ratio, and waterglass and fly ash contents. The cubic compressive strength increased with the decreases of water-to-binder ratio and fly ash content, and the increase of the waterglass content. Increasing waterglass content contributed to the improvement of the static compressive behavior of slag-based GC, such as elastic modulus and peak stress, while it led to the rise of the brittleness. Slag-based GC with different water-to-binder mass ratios, and waterglass and fly ash contents showed a strong strain-rate dependency. However, the inclusion of 50% fly ash induced a sharp increase of the dynamic compressive strength and dynamic increase factor (DIF) at a high strain rate. Moreover, both the two formulations for fitting static compressive stress-strain curve and DIF with higher accuracy were proposed in this study.

To investigate the influence of the fly ash (FA) content on the performance of high-performance concrete (HPC), seven groups of tests were conducted, aiming to evaluate both the macroscopic properties (workability and compressive strength) and microscopic pore structure. Low-field nuclear magnetic resonance (NMR) technology and SEM images were employed to analyze the changes in the internal pore structure of the concrete. The results showed that the workability of HPC initially increased and then decreased with the increase in the FA content. When the FA content was 15%, the slump of HPC reached a maximum of 264 mm, and the 28-day compressive strength exhibited a 23.2% increase compared to the 7-day compressive strength. The pore size distribution of the concrete varied with different fly ash content. At 15% FA content, secondary hydration of the FA was sufficient, refining the pores to between 0 and 0.1 µm. Excessive FA substitution deteriorated the internal structure of the HPC matrix and reduced the workability and mechanical properties of the HPC. When the content of FA was 35%, the slump of HPC decreased to 176 mm, while the macropores within the matrix significantly increased, resulting in porosity of 6.81%.

Experimental studies on the influence of oil shale fly ash additives on thermal expansion, strength, shrinkage, and heat release of concrete were carried out. The addition of 30% fly ash over cement content increases the thermal expansion by 6 times. The addition of 40% fly ash increases the thermal expansion by 16 times. The expansion is due to the high free calcium oxide content (10%) in the fly ash and the high sulfuric acid anhydrite SO3 content (10.3%). The anhydrite forms a highly expanding calcium hydrosulfoaluminate upon reaction with tricalcium aluminate cement in an unlimited amount of water. The oil shale fly ash addition above cement content significantly reduces shrinkage. If the ash content is higher, then the shrinkage decreases more. Shrinkage is on average 1.3 times less at a 30% fly ash content, and shrinkage is 1.8 times less at a 40% fly ash content. The fly ash has a higher sorption capacity than cement. Samples with the oil shale fly ash addition absorb more moisture than mixes without fly ash. Oil shale fly ash increases the compressive strength. If the fly ash content is 30% by weight of cement, then the compressive strength is higher than if the fly ash content is 40% by weight of cement for all concrete hardening periods. The flexural strength of mixes containing the fly ash turned out to be lower than the flexural strength of the mix without fly ash in the initial period of up to 15-22 days. Mixes with fly ash content in the amount of 30% and 40% by weight of cement exceeded the flexural strength of the mix without fly ash, respectively, by 24 and 17%. The fly ash addition provides a calmer, extended in time heat release with low self-heating of concrete in the initial period from 1 to 3 days. That is especially valuable for the thermal crack resistance of concrete.

Fly ash, a by-product of coal combustion in thermal power plants is utilized as a substitute for Portland Cement in concrete due to its pozzolanic properties. Mainly, class F fly ash—produced from the combustion of anthracite coal at approximately 1560˚C (according to SK SNI S15-1990-F)—contains less than 10% lime (CaO) and exhibits significant pozzolanic or filler properties. This research investigates the impact of varying fly ash proportions (0%, 10%, 15%, and 20%) on the compressive strength of concrete. The experimental setup included 108 cylindrical test specimens (10 cm in diameter and 20 cm in height), representing different brands of cement and fly ash mixtures, tested at 7, 14, and 28 days. The study was conducted at PT. Waskita Beton Precast Plant in Sadang, Purwakarta, West Java, targeting a concrete compressive strength of 40 MPa. Results indicate that at 0% fly ash, the compressive strength using Garuda Cement reached 76.66 MPa after 28 days. However, this strength decreased with increasing fly ash content, measuring 72.35 MPa, 69.07 MPa, and 68.13 MPa for 10%, 15%, and 20% fly ash, respectively. These findings highlight the influence of fly ash content on the structural integrity of concrete, suggesting a potential trade-off between sustainability and mechanical performance. Keyword: Fly Ash, Compressive Strength of Concrete, Portland Cement

This study aimed to investigate the characteristics of roller-compacted concrete when fine aggregate is replaced with fly ash. The investigation focused on assessing workability, compressive strength, flexural strength, and split tensile strength of the concrete mixtures. Four testing methods were employed, including the slump test for workability assessment, the compression test for determining compressive strength, the flexural test for evaluating flexural strength, and the split tensile test for measuring split tensile strength. The fly ash used in this project was sourced from the powerplant in Malaysia. Various fly ash contents, specifically 0%, 55%, 65%, and 75%, were utilized to replace the fine aggregate. The concrete mixtures were subjected to water curing for 7, 14, and 28 days before testing. Following the mixing process using a concrete mixer, the mixtures underwent a slump test to evaluate their workability. It was observed that the workability of the concrete decreased as the percentage of fly ash used to replace the fine aggregate increased. Mixtures with fly ash exhibited zero slump, while the control mixtures displayed true slump. Subsequently, compression, flexural, and split tensile tests were conducted after 7, 14, and 28 days of water curing. In terms of compression strength, an increase in fly ash content resulted in higher compressive strength in the concrete mixtures. The mixture with 65% fly ash content demonstrated the highest compressive strength at 49.84 MPa. Regarding flexural strength, the concrete with 75% fly ash content exhibited the highest value, measuring 5.45 MPa. However, for split tensile strength, the concrete without fly ash content showed the highest value at 8.84 MPa compared to other mixtures, indicating that the fly ash content exceeded the optimum amount for the mix design. In summary, the concrete mixtures with fly ash displayed several advantages, but their suitability depends on the specific type of construction.

The purpose of this study was to reveal that reconstructed soil composed of different types and proportions of materials has different effects on the growth of Melilotus officinalis, and to determine the most suitable formula of reconstructed soil materials to use for soil replacement. Using topsoil, coal gangue, fly ash, and rock and soil stripping materials from Shengli Mining Area of Inner Mongolia as raw materials, stratified and mixed pot experiments were carried out in a greenhouse using different proportions of each material. The differences in the aboveground biomass, leaf width, plant height, and root length of Melilotus officinalis plants in pot experiments were then compared using analysis of variance. The results showed that using different combinations of materials in different proportions affected the growth status of Melilotus officinalis, and their effects on biomass were greater than their effects on plant height, root length, and leaf width. When topsoil, coal gangue, and rock and soil stripping materials were mixed at a ratio of 3:3:4, respectively, the biomass of Melilotus officinalis increased by nearly 30% compared with that of plants potted in pure topsoil. When the content of coal gangue was controlled to be 30%, the content of fly ash was below 10%, and the content of rock and soil stripping materials was below 40%, the reconstructed soil conditions clearly promoted the growth of Melilotus officinalis. Coal gangue, rock and soil stripping materials, and fly ash can thus be used as substitutes for topsoil. Mixing soil reconstruction materials in the optimal proportion can solve the scarcity of topsoil in the grassland mining areas in the study region and, at the same time, can effectively improve the utilization of solid waste in this mining area.

Effect and limitation of free lime content in cement-fly ash mixtures

Despite many of the research studies on the effect of the particle size distribution of the sand and fly ash content on the mechanical behavior of the cement mortar, there has not been a comprehensive study investigating the effect of particle size distribution curve corresponding to 10% of finer (d10), fly ash content, curing time, sand particle size distribution properties (d10), and water to cement ratio (w/c) on the compressive (σc), tensile (σt), and flexural (σf) strengths of cement mortar. Therefore, this study investigates the subject which could be beneficial for the geotechnical and building and construction field. In this study, more than 1000 data on the mechanical properties of the cement mortar modified with different percentages of fly ash varied from 5 to 75% (by dry weight of the cement) collected from the literature. Statistical analysis and modeling were performed on the collected data. Vipulanandan p-q model was used and compared to the Logistic Growth model to predict the particle size distribution of sands used in the cement mortar. The water to cement ratio (w/c) of the cement mortar ranged between 0.20–0.80 percent and the compressive strength (σc), tensile strength (σt) and flexural strength (σf) of cement mortar modified with fly ash up to 90 days of curing were ranged between 15–88 MPa, 0.4–5 MPa, and 1–10 MPa, respectively. Vipulanandan correlation model was also used and compared with the Hoek–Brown model to correlate the mechanical properties of cement mortar modified with fly ash. The analysis and modeling results of the present study showed that there is a good relationship between the compressive strength (σc) with w/c, curing time, fly ash content and d10. Based on the coefficient of determination (R2) and root mean square error (RMSE) the compressive strength (σc), flexural strength (σf) and tensile strength (σt) of cement mortar quantified well as a function of w/c, the percentage of fly ash, curing time, and d10 using nonlinear relationship.

Sustained research and development work on the utilization of waste (fly ash and silica fume) for various productive uses have been carried out. In the construction industry, major attention has been devoted to the use of fly ash and silica fume in concrete as addition to or as cement replacement. The utilization of a solid waste, fly ash and silica fume, in polymer concrete was reported in this paper including the effects on the compressive strength, flexural strength, and split tensile strength. The results show the influence of fly ash and silica fume content on the mechanical properties of polymer concrete with epoxy resin. The fillers improved the mechanical characteristics of polymer concrete compared to that of polymer concrete without filler: the compressive strength of polymer concrete with fly ash content was favorably influenced by the filler compound to polymer concrete with silica fume.

High volume fly ash concrete becomes one of alternatives to produce green concrete as it uses waste material and significantly reduces the utilization of Portland cement in concrete production. Although using less cement, its compressive strength is comparable to ordinary Portland cement (hereafter OPC) and the its durability increases significantly. This paper reports investigation on the effect of design strength, fly ash content and curing method on compressive strength of High Volume Fly Ash Concrete. The experiment and data analysis were prepared using minitab, a statistic software for design of experimental. The specimens were concrete cylinder with diameter of 15 cm and height of 30 cm, tested for its compressive strength at 56 days. The result of the research demonstrates that high volume fly ash concrete can produce comparable compressive strength which meets the strength of OPC design strength especially for high strength concrete. In addition, the best mix proportion to achieve the design strength is the combination of high strength concrete and 50% content of fly ash. Moreover, the use of spraying method for curing method of concrete on site is still recommended as it would not significantly reduce the compressive strength result.

To study the effect of double mixing of waste rubber and fly ash on the strength and water permeability of pervious concrete, this paper adopts an orthogonal experimental design, aiming at exploring an optimal range between the mixing amount of waste rubber and fly ash by analyzing the effect of different mixing amounts of the two on the compressive strength and water permeability coefficient of the pervious concrete and analyzing the design of the mixing ratio with an optimized balance of strength and water permeability coefficient. The results show that an appropriate amount of fly ash can improve the compactness and compressive strength of concrete, but too much will reduce the compressive strength. Waste rubber can increase the compressive strength within a certain mixing range, but too much will reduce it. The water permeability coefficient decreases with the increase in the dosage of waste rubber and fly ash. It was found that the best overall performance of pervious concrete was achieved when the water-cement ratio was 0.28, at 15% fly ash and 10% waste rubber. This study provides a new type of road material for the practical application of previous concrete, which helps to solve the problem of waste tire pollution and promotes the development of green building materials.