Fine Aggregate Ratio Research Articles

Electrical resistivity of eco-friendly hybrid fiber-reinforced SCC: Effect of ground granulated blast furnace slag and copper slag content as well as hooked-end fiber length

Over the last 20 years, the development of electrically conductive composites for removing snow and ice from transportation infrastructure has received exceptional traction. However, these composites need to exhibit stable electrical conductivity and high mechanical properties to be sustainable and cost-effective. Towards this goal, the article investigates the roles of ground granulated blast furnace slag (BFS) and copper slag (CS) content, in addition to hooked-end steel fiber length, on the electrical properties of eco-friendly ultra-high performance hybrid fiber-reinforced self-compacting concrete (HFR-SCC) for the first time in the literature. For this purpose, sixteen eco-friendly electrically conductive ultra-high-performance HFR-SCC were designed based on the variable parameters of four different BFS/total binder ratios (20, 40, 60, and 80 %), a CS/total fine aggregate ratio of 50 %, and two different hooked-end fiber lengths (30 and 60 mm), while all mixes used 1.75 % by volume fraction of steel fibers. After determining the workability properties (slump-flow and T500 values) of all mixes, compressive strength and electrical resistivity/conductivity tests of 90-day specimens were conducted. Additionally, environmental and economic evaluations of all mixes in terms of sustainability were performed in order to clarify the effects of the variable parameters. Taking into account the experimental results obtained, it was observed that all electrically conductive ultra-high performance HFR-SCC mixes demonstrated satisfactory workability properties, while the compressive strength values reached to impressive values of 127 MPa. The optimum BFS/total binder ratio was identified to be 40 % for higher compressive strength and conductivity of ultra-high performance HFR-SCC specimens. On the other hand, the addition of CS to the mixes resulted in an increase of almost 9 % in compressive strength compared to one without CS, while at the same time, a significant increase of approximately 363 % was observed in the electrical conductivity values of the specimens. As for the influence of different lengths of hooked steel fibers, the use of 30 mm length hooked-end steel fibers in HFR-SCC mixes performed better in terms of compressive strength, whereas 60 mm fibers performed better regarding electrical conductivity. In conclusion, this experimental work has evidenced that it is possible to develop an eco-friendly and sustainable electrically conductive ultra-high performance cementitious composite (the optimal mix compressive strength and electrical resistivity values were 127 MPa and 2242 Ω.cm, respectively) by using waste from different industries such as iron and copper. Thus, it will provide important insights for the design and application of future electrically conductive concretes, which can be an important alternative in efficient active deicing and snow-melting applications.

DEVELOPMENT OF DRY MIX MORTARS FOR FLOOR ELEMENTS

Dry mix mortars are widely used in construction projects for the implementation of construction works in new construction, reconstruction, and repair. The improvement of properties of dry mix mortars for the installation of floor screeds is relevant. The purpose of such mortars is to equalize the differences in the thickness of the floor surface, to create an intermediate layer characterized by the necessary strength, durability, and even surface with the possibility of decoration with various types of flooring. A step-by-step design of the composition of dry mix mortar for the installation of floor screeds was carried out. The ratio of fine aggregates and limestone filler was optimized according to the maximum packing density criterion, the required amount of plasticizer was selected according to the consistency index of the fresh mortar, and the minimum amount of Portland cement was selected to ensure the required strength.

Utilization of municipal solid waste incinerator bottom ash (MSWIBA) in concrete as partial replacement of fine aggregate

Enhancing sustainable economic development while maintaining environmental integrity is of paramount importance. In this context, the effective utilization of municipal solid waste incinerator bottom ash (MSWIBA) presents a significant opportunity. This study investigated an approach for harnessing the potential of MSWIBA by incorporating it as a partial replacement for fine aggregate in concrete mixtures. Twelve concrete samples were prepared with varying proportions of MSWIBA. The mechanical and microstructural properties of the samples were comprehensively investigated. Moreover, the environmental and economic advantages of these concrete formulations were assessed. The results revealed that the water absorption of the concrete samples without MSWIBA was higher than that of the concrete samples with MSWIBA, suggesting that the added MSWIBA could fill the internal pores of concretes. The water absorption rate curve could be divided into three stages, i.e., rapid decline, slow decline, and stable. The optimal replacement ratio of fine aggregate with MSWIBA was between 24.8% and 57.8%. Notably, when the replacement ratio surpassed 24.8%, MSWIBA positively influenced the development of compressive strength, but it still lower than that of composite Portland cement-based concrete (OPC). Furthermore, pore structure analysis indicated that the efficacy of pore refinement was achieved within a certain replacement threshold. However, the efficacy of pore structure refinement diminished beyond that threshold. The substitution of fine aggregate with MSWIBA aligns with the technical specifications and building material standards, thereby complying with the principles of effective utilization, sustainability, and environmental consideration pertinent to MSWIBA management.

순환골재가 고유동 콘크리트의 유동특성에 미치는 영향

The purpose of this study was to promote the use of recycled aggregates by using recycled aggregates as aggregates for high flowing concrete. The recycled aggregate used in this study was made by curing concrete with a Fck 40 MPa for 6 months and then crushing it using a Jaw crusher. To evaluate the properties of high flowing concrete using recycled aggregates, various concrete mixture conditions such as replacement rate of the recycled aggregates, W/B and Volume ratio of fine aggregate(Sr) were reviewed. Slump flow test, L-funnel flow test and funneling test were conducted to estimate flowability, resistance to segregation and fillingability. As a result, the mixture conditions of high flowing concrete using recycled aggregate to satisfy the required performance could be found; the replacement rate of the recycled aggregate of below 50%, W/B of below 37% and Sr of below 47%.

Mechanical and durability properties of standard and high strength geopolymer concrete using particle packing theory

Aggregate packing significantly affects the characteristics of fresh and hardened concrete; aggregates having higher packing density (PD) improve these characteristics. There is a lack of research on how the PD affects the properties of geopolymer concrete (GPC). Hence, the present study includes the effect of the PD on the mechanical and durability properties of the standard and high-strength GPC. The study parameters are the binder content, the concentration of NaOH, and the fly ash to ground granulated blast furnace slag (GGBS) ratio. Six aggregate groups (like 12.5–10 mm, 10–4.75 mm, 4.75–2.36 mm, 2.36-1.18 mm, 1.18–0.6, and 0.6–0.15 mm) were investigated for the particle packing experiment, and the blended coarse:fine aggregate ratio of 55:45 which produced the highest packing density of 0.702, were used in the GPC mixes. A total of 120 cubes of size 100 mm, 30 cylinders of size 100 × 200 mm, and 30 prisms of size 100 × 100 × 500 mm were cast for 10 different mixes in the study. Sorptivity and water absorption are the tests performed for the durability studies. The result shows that GPC mixes with Particle packing theory significantly improved the compressive strength, and durability, and showed better workability. The workability of the GPC reduces by increasing the GGBS and concentration of the NaOH solution. As the GGBS proportion and the concentration of the NaOH solution increases, the concrete compressive, split, and flexural strength increases. As the binder content increases, the strength increases at first, then reduces. Increasing the GGBS content, binder content, and molarity of the NaOH accomplishes a reduction of the sorptivity coefficient and water absorption of the GPC.

Feasibility study on impact of replacement of river sand with crushed aggregate in concrete mix

The importance of utilizing stone waste, known as stone dust, in construction and infrastructure projects as a replacement for natural sand cannot be overstated. This practice holds paramount significance as it not only serves to substitute natural sand but also plays a pivotal role in reducing construction expenses. Because of the severe shortage in many locations, as well as expense and environmental concerns, an alternative is being considered. In this endeavor, the viability of incorporating stone dust as a potential substitute for fine aggregate is under meticulous investigation. In this study, M20, M30, and M40 concrete mixes were employed. The results of the tests show that stone dust may be utilized in concrete as a partial replacement for fine aggregate. The finding has been made that using stone dust increases the flexural and compressive strength of concrete. The percentage of fine aggregate replaced by stone dust (0, 20, 50, 80, and 100 percent) is explored. This paper also studied various proportions of cement concrete and stone dust (M20, M30, M40). The experimental findings revealed that adding stone dust as a fine aggregate ratio of 20%, 50%, 80%, and 100% improved the compressive properties.

Study of fly ash-slag geopolymer mortar as a rapid strengthening agent for concrete structures

A fly ash-slag geopolymer mortar (GPM) was developed as an efficient bond material for rapidly strengthening concrete structures. To determine the most significant factors affecting fluidity, setting time, and early compressive strength, we studied the following six factors using an orthogonal test: the amount of slag in the binder (SL/B), the mass ratio of sodium silicate to sodium hydroxide (SS/SH), the molarity of NaOH (MN), the mass ratio of alkali solution to binder (A/B), the superplasticizer addition to binder (SP/B), and the mass ratio of fine aggregates to binder (F/B). Different admixtures have been studied to improve the fluidity of the GPM. Bonding tests were conducted to investigate the differences in the bond behavior of the GPM. The results indicate that SL/B and A/B significantly affected the properties of the GPM. Increasing SL/B was beneficial for enhancing the early compressive strength of the GPM and decreasing its fluidity and setting time, whereas A/B exhibited the opposite trend. It is challenging to meet the requirements of high early strength and fluidity of the GPM by only changing the chemical composition, and admixtures should be added. The 1-day GPM without the interfacial agent exhibited a bond strength similar to that of the PCM at 7 days and the existing interfacial agent was not suitable for the early-strength GPM.

Use of crushed bricks and recycled concrete as replacement for fine and coarse aggregates for sustainable concrete production

The growing concern over the significant ecological changes requires sustainable developments in all fields. Concrete production is one of the largest consumers of natural resources as it consumes a huge volume of natural fine and coarse aggregates, which constitute 70% - 80% of the concrete volume. It is evident that such large amount of concrete production in the growing construction industry puts significant impact on the use of natural resources and the environment. Hence, investigating the use of recycled materials to replace the finite natural resources became evident and is the focus of researchers. In this research, the use of waste crushed bricks (CB), and crushed recycled concrete (CRC) as a partial replacement of fine and coarse aggregates in concrete was studied. The replacement ratios of 10%, 50%, and 100% by weight of either fine or coarse aggregates were used. Eight concrete mixes with 168 specimens were tested for compressive, splitting tensile as well as, flexural strength. All tests were carried out at ages of 7, 28 and 56 days. The results indicated that there is a feasibility of using bricks and concrete wastes in concrete mix as a partial replacement of course and fine aggregates. It is deduced that a 50% replacement ratio of coarse aggregate with crushed concrete resulted in a 30%, 25%, and 23% increase in compressive, tensile, and flexural strengths, respectively. While 50% replacement ratio of fine aggregate with crushed bricks resulted in a 23%, 28%, and 19% increase in compressive, tensile, and flexural strengths, respectively. The most effective mix was at 50% replacement ratio of coarse aggregate with crushed concrete in combination with 50% replacement ratio of fine aggregate with crushed bricks. The results of this mix showed 32%, 28%, 26% increase in compressive, tensile, and flexural strengths, respectively.

The compressive strength and the setting time of partial replacement of fly ash by palm oil fuel ash on geopolymer paste and mortar

This study replaced fly ash with palm oil fuel ash (POFA) in geopolymer paste and mortar. The alkaline activator was a mixture of sodium silicate solution and sodium hydroxide solution with a ratio of 2.5. Three variables were evaluated: the raw material combination (100% fly ash and 25% POFA substituted to fly ash), the mass ratio of raw material to alkali activator (60/40, 65/35, and 70/30), and NaOH molarity (8 M and 10 M). The geopolymer mortar was utilized based on the highest compressive strength of geopolymer paste. The ratio of fine aggregate to binder was 65 to 35. The result showed that the compressive strength of geopolymer paste increased as NaOH molarity increased. 25% substitution of POFA for fly ash increased the compressive strength of geopolymer paste from 12.0% to 27% at 28 days. The raw material/ alkali activator ratio of 65/35 indicated the highest compressive strength. The POFA replacement for fly ash had a longer setting time than 100% fly ash. The compressive strength ratio of mortar to the geopolymer paste was 0.66 and 0.59 for the 65/35 and 70/30 ratios of raw material to alkali activator, respectively.

Ecological impact assessment of sustainable concrete paver blocks based on endpoint damage categories

Cement concrete is said to be a versatile material but its sustainability is always questioned. There exists a huge scope to improve the sustainability of traditional concrete as its primary binding ingredient i.e., cement is responsible for a huge amount of carbon dioxide production. Since now-a-day footpaths, roads and parking etc. places are being renovated and constructed with concrete paver blocks instead of traditional methods like flexible pavements this also has increased concrete usage. Paver block making concrete is very different from structural concrete owing to the ratio of fine aggregate to coarse aggregate as per Indian code’s provisions and since there is a difference in composition, there will be difference in ecological impacts. In India, various industrial by-products are being generated out of which fly ash and bagasse ash are two of many, which are produced during the electricity generation in the plants. There exists a perennial problem associated with the disposal issue of these materials. Life cycle assessment is a method that is used to evaluate the ecological impacts of the materials where impacts can be evaluated at midpoint levels as well as endpoint levels. In this study, four types of concretes e.g., traditional concrete, fly ash-based blended concrete and two geopolymer concretes (one with only fly ash as precursor, second with binary blend of fly ash and sugarcane bagasse as precursor) were prepared for the production of paver blocks and comparison of their ecological impacts thereof which was studied at the endpoint damage categories. Results from this study showed that cement-based traditional concrete blocks were much more harmful as compared to other concrete blocks in all the damage categories.

Experimental study on RPC containing zircon sand and sillimanite at elevated temperatures

The main purpose of this project involves investigation of Reactive Powder concrete (RPC), known for its ultra-high strength and improved durability properties and the influence of elevated temperatures compared with that of standard water cured samples in RPC. The process of binding is taken care by high alumina cement. The various material propositions of RPC includes Quartz sand, zircon sand, sillimanite and alccofine were used to achieve low level porosity with dense concrete matrix, thereby eliminating the addition of coarse aggregates. Micro steel fiber were used to improve the tensile property in concrete composite. The workability of concrete is improved based on poly carboxylate based super plasticizer. The experimental investigation comprises of eighteen specimens were cast and its compressive strength was observed. The samples are said to the replacement of cement with that of HAC and Alccofine in a constant ratio. The fine aggregate are being replaced completely by quartz sand, zircon sand and sillimanite with varying ratio. The samples undergone standard water curing and heat treatment at temperatures 150 °C, 300 °C, 450 °C and 600 °C. The comparative results between the standard water curing and heat treatment is observed for varying ratio of fine aggregate along with micro steel fiber and super plasticizer and the results are recorded.

Powder-bed-based 3D printing with cement for sustainable casting

3D printing allows for the cost-effective fabrication of moulds and can cast complex shapes. In this study, alumina cement and fine aggregates for refractories were used as the main raw materials, and saturation was adjusted to an appropriate level to control the cement binder mixture for sand casting. For cast iron, the mould must withstand temperatures of up to 1400 °C and must exhibit sufficient strength, gas permeability, and thermochemical durability at high temperatures. To accomplish these requirements, 3D printing powder was prepared by adjusting the ratio of fine aggregate (D50: 30 μm) and an even finer cement component (D50: 4 μm). To improve the moulding quality, a green body was used to optimise the cement admixtures to increase the strength, and the saturation level of the 3D printer was adjusted for dimensional accuracy. The high-temperature durability of the mould was evaluated by measuring its strength after heat treatment, using Simultaneous Thermal Analysis (TG-DSC), and through dimensional stability assessment. In addition, the pores of the specimens were analysed through microscale X-ray tomography. The surface resolution and tolerance of the final casting were determined by a 3D image roughness test using a surface roughness scanner. The cement exhibited the shortest curing time and the highest strength when the mass ratio of CA (CaO·Al2O3) to C12A7 (12CaO·7Al2O3) was 8:2. The final mixing mass ratio of cement to the fine aggregate was 8:2, which was determined based on the relationship between flowability and powder bed surface quality. The results proved the high-temperature thermal stability of the 3D-printed mould, which showed a total mass reduction of less than 3% and a low coefficient of linear expansion up to 1300 °C. Consequently, the suitability of the 3D-printed moulded body, composed of casting sand with cement as a binder, for casting at temperatures >1400 °C was demonstrated. Additionally, the final printed porous mould de-powdered easily, and its recyclability was verified by strength testing various mass ratios of fresh and recycled powder. Therefore, through optimisation of the material combinations and adjustment of the 3D printing process parameters, optimal gas permeability and moulding resolution could be achieved without any casting defect, while maintaining handling strength. The findings of this study demonstrate the potential of expanding the scope of powder-bed-based 3D printing of cement material to the casting market.

Using GA - BP Coupling Algorithm to Predict the High-performance Concrete Mechanical Property

As a cementitious composite, concrete's property depends on the matrix generated from cement hydration and the dispersed phases such as aggregates. Compression strength is an important mechanics performance index of concrete quality, especially the High-performance Concrete (HPC). However, owing to the expensive cost of test and the existence of high-dimensional nonlinear mapping between compression strength and basic materials, it is uneasiness to precisely forecast the compression strength value of HPC by general formula method. In this research, a novel machine learning system, Genetic Algorithm and BP Neural Network (GA-BPNN) coupling algorithm, is offered to predict the compression strength of HPC. GA-BPNN coupling algorithm model used 181 groups of HPC mixture data to determine 8 factors affecting its compression strength (i.e., Water, Portland Cement, Waterbinder Ratio, Fine Aggregate Ratio, Air-entraining Agent, Fly Ash, Silica Fume, and Superplasticizer) as the input variables of the model, while compression strength was set as the output variable. In addition, 166 sets of training set data were segmented into training, validation and test set again, and BP neural network (BPNN) was compared with GA-BPNN to verify the generalization capacity of the model in this research. By forecasting the compression strength of 15 test sets, the average relative error is only 0.902%. Finally, the sensitivity of input variables of GA-BPNN model was analyzed by using Gray Relational analysis (GRA) method. Six models were established to research the impact of sensitivity and quantity of input variables on model performance by ignoring individual input variable. The research is shown that GA-BPNN model not only has the powerful nonlinear mapping ability of BPNN, but also has the global search optimization ability of GA, and showed stronger robustness and prediction potential in the assessment of compression strength value of HPC. The sensitivity analysis shows that, to compression strength of HPC, Cement, Water and Water-binder ratio has a sensitivity score of 0.8166, 0.70122, 0.66772, respectively while Fly Ash has the lowest sensitivity.

A scientometric review on mechanical and durability performance of geopolymer Paste: Effect of various raw materials

• An extensive review on geopolymer paste (GPL) for mechanical and durability behavior. • Microstructural assessment of fly ash (FA) and FA-slag GPL paste. • Assessment of different properties of GPL for various raw materials. • Assessment of durability performance of GPL for various raw materials. Geopolymer (GPL) paste has recently become a promising ecological substitute for conventional cementitious composites. They are environmentally friendly and cost-effective, and their manufacture involves a relatively small amount of energy. GPL is alkali-activated pastes made up of base materials that can be utilized for concrete structures, ensuring environmental sustainability and enabling cost-effective construction. This research assesses the microstructural aspects of fly ash (FA) and FA-slag GPL paste, fresh characteristics including workability and setting time, hardened characteristics including compressive strength (CS), and splitting tensile strength (STS), and durability characteristics. The influence of various forms of alkaline solution, the concentrations of alkaline solution, the integration of various kinds of alkaline activators, the alkaline solution to the binding material ratio (S/B), the ratio of fine aggregate to binding material, curing duration and temperature, and the influence of multiple kinds of superplasticizers are investigated. The current work also examines the influence of several additives in FA-GPL and FA-slag GPL pastes, including nano-materials, different kinds of fibers, bio-additives, epoxy, alumina, quartz powder, alccofine, and silica fume (SF). The influence of mix proportioning on the durability, hardened, and fresh features of FA-GPL and FA-slag GPL mix was comprehensively discussed in this work. The conclusions of the reviewed research papers are reported comprehensively.

Effect of moisture content and mix proportion of concrete on efficiency of laser scabbling

Laser scabbling is one of the options that can be used for removal of contaminated concrete when decommissioning and dismantling of nuclear power plant. Laser scabbling can be advantageous for such purpose because laser can transmit through long-distance and the system operates remotely in dry condition while minimizing the human access to the radioactively contaminated area. In order to investigate the applicability of laser scabbling on concrete, the experimental program was conducted on concrete with various moisture content, fine aggregate ratio with different paste content. According to the results, concrete in oven dry condition showed no efficiency on laser scabbling. The surface of the concrete was vitrified as a result. However, a 5 kW fiber laser with 900 mm stand-off distance was successfully applied for laser scabbling of air dry and saturated surface dry concretes. It was found that the moisture is a prerequisite requirement for successful laser scabbling of concrete. The changes in fine aggregate ratio and paste content did not affect the efficiency of laser scabbling.

Aggregate Simulation with Statistical Approach Considering Substituting

This work focused on reflecting the substituting ratio of fine aggregate in an aggregate simulation. The existing simulation studies showed superior performance on generating the particles; however, the studies did not and could not reflect the substituting ratio of fine aggregate. Therefore, a statistical approach with the Monte Carlo simulation method was tried to improve the lacking part. According to the fitting of the distributions, the Cauchy distribution was best for the natural sand and the log-normal distribution was best for the substituting materials. The chosen two distributions were mixed and applied, using the Monte Carlo method with the mixed model, rather than the existing particle generation formula of the simulation. The substitution ratio was considered to be 0, 30, 50, 70, 100%. The fraction of small particles was gradually increased by the substituting ratio. As a result, the simulated particle distribution reflected well the statistical model. In addition, the simulation was almost the same as that of real particle distribution, according to the CT scanning.

Properties of nano silica modified cement less geopolymer composite mortar using fly ash and GGBS

Geopolymer concrete/mortar has been gaining attention worldwide since it has become an alternative option to overcome various sustainability and environmental related problems associated with construction as the source material fly ash is obtained as a byproduct due to the firing of coal in power stations. In the present study, geopolymer mortar was synthesized using the pozzolanic source materials like fly ash blended with Ground Granulated Blast Furnace Slag (GGBS) along with alkaline activator liquids with inclusion of different percentages of nano silica. Relevant test standards were used to determine the fresh characteristics of geopolymer mortar such as time for initial setting and workability. The hardened properties like flexural strength, compressive strength and water absorption were also explored. Parameters like the ratio of fine aggregate to pozzolanic material and the ratio of alkaline activating solutions to pozzolanic material are correspondingly 1:1.5 and 0.4:1. Alkaline solutions consist of one part of Sodium Hydroxide (NaOH) and 2.5 parts of Sodium silicate (Na2SiO3). The pozzolanic material is composed of 10% of GGBS and 90% of fly ash. Five mixes were prepared by adding nano silica as an additive in 0%, 1%, 2%, 3%, and 4% by weight of cementitious material. Mortar samples were prepared and cured under ambient conditions for various tests. Addition of Nano silica by 1% to the mortar mix contributes positively to various properties of geopolymer mortar.

Manufacture and Engineering Properties of Cementitious Mortar Incorporating Unground Rice Husk Ash as Fine Aggregate

This study investigates the manufacture and engineering properties of cementitious mortar incorporating unground rice husk ash (URHA) as fine aggregate. Six mixtures of mortar were produced with using URHA to substitute for crushed sand in amounts of 0%, 20%, 40%, 60%, 80%, and 100% by volume at constant water-to-powder ratio of 0.6 and volume ratio of fine aggregate to powder of 2.5. The experimental series consisted of the flowability, density, water absorption, compressive strength, flexural strength, dynamic modulus of elasticity, ultrasonic pulse velocity, and scanning electron microscopy tested under relevant standards. The fresh and dried densities of mortar with URHA significantly reduced from 5% to 29% and from 8% to 39%, respectively, compared to mortar without URHA. The higher ratio of URHA to fine aggregate led to a darker color, and higher water absorption of cementitious mortar. Replacing of 20%–40% fine aggregate volume by URHA produced mortars with comparable compressive strength at later ages. The flexural strength, dynamic modulus of elasticity, and ultrasonic pulse velocity values of mortar presented the downtrend with increase of URHA content; however, the developing rate of these values was meaningfully promoted at later ages due to internal curing and pozzolanic action. The present study supported the technical feasibility and environmental friendliness of cementitious mortar produced with replacing the natural fine aggregate up to 100% in volume.

Influence of Composition Parameters, Curing Conditions and Salt Solutions on Geopolymer Concrete Properties.(Dept.C)

The growing demand for environmentally friendly construction has been the driving force behind the production of sustainable and cost-effective construction materials. Portland cement (PC), which is not considered an environmentally friendly material, is an important ingredient in concrete. In contrast to Portland cement, geopolymers are gaining increased interest as low-CO2 emission binders. This research consists of two basic stages, the first stage investigates the effects of many parameters on the properties of geopolymer concrete based on fly ash, in particular the compressive strength, tensile strength, and flexural strength .The parameters included were fly ash content, degree of solution molarity, alkaline liquid ratio to fly ash content, curing conditions, fine aggregate to coarse aggregate ratio. Second stage of the research concerned with the durability of geo-polymer concrete developed using fly ash class-F. As a guide for assessing the durability of geo-polymer concrete, the efficiency of ordinary Portland cement (OPC) concrete is also discussed. The influence of salt solutions of different concentrations through various periods of wetting – drying cycles on the weight loss, water absorption, and geo-polymer concrete has been investigated for its compressive strength. According to the first stage results, the best parameters which gave the highest geo-polymer concrete's mechanical properties, were: fly ash content of 400 kg/m3, 16 M degree of molarity, curing time of 3 days in oven, the ratio of alkaline liquid to the content of fly ash equals 0.5 and ratio of fine aggregate to coarse aggregate equals to 1:2, where the compressive strength reached its highest value (387 Kg/cm2). The results of second stage revealed that geopolymer concrete is less affected than cement concrete with respect to compressive strength and more affected in weight loss and water absorption. Geopolymer concrete showed an increase in water absorption compared to OPC concrete, after 9 weeks of wetting – drying cycles in salt solutions, by about 176% &184% for 5% & 10% solutions concentration, respectively. Also, more weight loss for geopolymer concrete specimens was revealed compared to OPC concrete by about 33% & 30% for 5% & 10% solutions concentration, respectively. However, the geopolymer concrete (GPC) showed less reduction in compressive strength due to the exposure to salt solutions (wet – dry cycles) than OPC. For both solution concentrations (5% & 10%), the average reductions in GPC compressive strength were 18%& 25%, respectively, while the corresponding reductions in OPC were 25% & 34%.

Effect of aggregate content on the CFRP-concrete effective bond length: An experimental and analytical study

Despite the wide range of proposed models in construction codes for estimating the carbon fiber reinforced polymer (CFRP)-concrete effective bond length, no attention has yet been given in the codes regarding the effect of aggregate content on effective bond length. The current study investigated the above-mentioned issues with varying volumes of coarse aggregates based on the concept of ‘sand ratio’ defined as the ratio of fine aggregate volume-to-total aggregates’ volume in concrete. For this purpose, 52 single-lap shear tests were conducted in two main groups of 23 and 35 MPa compressive strengths of concrete. Analytical and experimental results revealed that the effective bond length increased by 54% by increasing the sand ratio from 0.34 to 0.70 for the first group. However, the effective bond length demonstrated a 26% reduction by increasing the sand ratio from 0.70 to 1.00. Regarding the second group, the effective bond length increased by 45% by increasing the sand ratio from 0.29 to 0.62, while the effective bond length represented a 40% decrease by increasing the sand ratio from 0.62 to 1.00. Finally, the results indicated the necessity of correction factors in code models to explain the sand ratio effect. Such correction factors were extracted to be applied to the code models.