Aggregate Ratio Research Articles

Mechanical and bond behaviour of high volume Ultrafine-slag blended fly ash based alkali activated concrete

The development of Geopolymer concrete (GPC) mixes by employing large volume of ultrafine ground granulated blast furnace slag (UBFS) blended with Fly ash (FA) and activated by sodium hydroxide (SH) has been presented in this study. Several GPC mixes has been prepared to investigate the effect of varying alkali content, fine aggregate to total aggregate ratio (s/a) and molar concentration (M) of alkali activator on the fresh and hardened characteristics, including the bond strength with Portland cement concrete (PCC). The properties of the GPC mixes are assessed by workability test, compressive strength test, split tensile strength test and slant shear test, including the microstructure through FESEM (Field Emission Scan Electron Microscopy) and X-ray diffraction (XRD). The test result shows that s/a ratio is a crucial factor in controlling segregation and bleeding in GPC. However, an ideal GPC mix with s/a ratio 0.41 provides a better packing resulting in improved mechanical properties. Application of high volume UBFS in the GPC exhibits better reaction products as shown by the microstructure at a relatively lower alkali concentration which ultimately leads to higher strength. Superior bond strength is achieved between the GPC and old PCC substrate; however, the molarity of SH significantly affects the adhesion property of GPC.

Scanning through multidisciplinary techniques and recreation of historic mortar: Case study of Rohtas Fort

Rohtas fort built by Sher Shah Suri is located in Jhelum district of Punjab province in Pakistan. It is a national heritage as well as a UNESCO world heritage site. With the passage of time, Rohtas fort had seen significant deterioration. One of the major deteriorations affecting Rohtas fort the most is the decay of the mortar, which results in stone loosening in the stone masonry walls. The objective of the study is to analyze the mortar samples taken from Rohtas fort and suggest a repair material, which is compatible with the old Mortar. This work was divided into two parts; the first one consisted of the characterization of the old mortar and the second part as design of a modern-day mortar made from similar ingredients. The old mortar was evaluated through a number of multidisciplinary techniques like density, porosity, compressive strength, microscopic examining, XRD, XRF and TGA. The analysis revealed that the old mortar consisted of hydrated lime, broken bricks, sand and clay. The hydrated lime: aggregates ratio was found out to be 1.156. The density, porosity and compressive strength of the old mortar was found as 1.6 g/cm3, 42% and 2.2 MPa. The presence of Calcium-Silicate-Hydrate (C-S-H) gel revealed pozzolanic activity due to brick particles. The modern mortar was prepared with the same ingredients, hydrated lime, local brick particles, local sand and local clay in the composition analogous to that of the old one. The particle size distribution of the aggregates was also kept same as that of the old mortar. The density, porosity and the compressive strength of the modern mortar was found to be 1.9 g/cm3, 35% and 3.5 MPa respectively at 28 days of age. Owing to pozzolanic character of the brick particles, and carbonation of the hydrated lime, the properties are expected to improve further.

Multi‐objective optimization and assessment of recycled concrete aggregates for sustainable development: Example of the Kömürhan bridge

AbstractThe main purpose of this study is to examine the advantages and disadvantages of the Kömürhan bridge, built with natural aggregate concrete in Elazig, in terms of mechanical, environmental, and economic properties if certain ratios of recycled concrete aggregate (RCA) were used. For this purpose, a detailed laboratory study was designed, and concrete samples were produced, all‐natural, all‐recycled, and both recycled and containing natural aggregates. Different water‐to‐cement, aggregate‐to‐cement, and recycled concrete aggregate‐to‐total aggregate ratios were considered for the mixture designs of these samples, and the fresh and hardened concrete properties of these samples were determined. Then, statistical analyses were made using the response surface method, and numerical models were developed to predict the fresh and hardened concrete properties with high accuracy. Mixtures containing RCA, which have the same fresh and hardened concrete properties as the fresh and hardened concrete properties of the Kömürhan bridge, which was selected as an example structure by using these models, were determined for optimization purposes. A detailed environmental and economic comparison of the optimization and reference mixtures was made. While making environmental assessments, energy consumption, global warming potential, waste generation, and abiotic depletion were considered. It was seen that the optimization mixtures were more economical and more environmentally friendly than the reference mixture. As a result of this study, it was predicted that the use of RCA in buildings constructed using large amounts of concrete could provide significant environmental and economic advantages and was exemplified by the Kömürhan bridge.

Investigation of mechanical and insulation properties of Sorel cement binding light concrete

In this study, some mechanical and insulation properties of light concrete with Sorel cement were investigated by using Sorel cement, which is an alternative to cements used in the market. In addition, samples were produced by substituting some additives separately into the Sorel cement mixtures in order to evaluate the waste materials in the inactive state and to improve some of the mechanical and insulation properties of the Sorel cemented samples. In this study the flexural and compressive strengths, thermal conductivity, thermal resistance, ultrasound transition velocity, unit weight, water absorption and apparent porosity, bulk expansion, alkali silica reaction (ASR), surface area analysis (BET) and microstructures of samples were investigated. The reference samples were Sorel cement (SC), the other samples were made of mixtures of SC, pumice (P), air-entraining additive (AEA), Afşin Elbistan fly ash (AEFA), wood and corncob shavings (WS, CS). According to the findings, it can be said that while the flexural and compressive strength of the lightweight aggregate samples decreased compared to the reference sample, there were improvements in heat and sound insulation properties. The determined values differed according to the type and ratio of lightweight aggregates. It was observed that the increase in the ambient temperature of the SC samples had a positive effect on the flexural and compressive strength values up to 100 °C, while it caused a decrease in the strength values after a certain temperature. It was seen that the strength values of SC samples kept in water decreased due to the cracks formed. The results showed that the samples produced with Sorel cement had high strength. Sample strengths produced with pumice used as aggregate are higher than those with wood chips and corncob sawdust. It was determined that Sorel cement could not be used together with AEFA because the samples were shattered. No incompatibility was observed with AEA and WS additives either; however, the strength value was low in those with CS added.

Thermal conductivity, abrasion resistance and compressive strength of end-of-life tire aggregate incorporated concrete

Recycling end-of-life tires is a global problem that requires an urgent solution. Storing and preserving these tires is a challenge that delays facing potential problems instead of solving the problem. In this context, recycling waste tires without harming the environment and at low costs has been the focus of many researchers. For several decades, the possibility of grinding these tires to aggregate size for concrete and substituting them with natural aggregate has been the subject of research by scientists working in this field. In this regard, this study aims to experimentally investigate the influence of waste rubber aggregate on some engineering properties of concrete, such as ultrasonic pulse velocity-based quality assessment, abrasion resistance, thermal conductivity characteristics, and mechanical performance, namely, compressive strength. Another significant side of the study was establishing a statistical relationship and correlation between the w/c ratio and substitution level of waste rubber aggregate and the experimental outputs. The experimental study indicated that the waste rubber aggregate decreased the concretes' compressive strength, but it improved the thermal conductivity characteristics and abrasion resistance of the concretes manufactured in this study. On the other hand, the statistical analysis revealed that the input parameters have meaningful effects on the engineering properties of the concretes, and there is a strong correlation between these properties.

Aggregation Interface and Rigid Spots Sustain the Stable Framework of a Thermophilic N-Demethylase.

Enzymes from thermophilic microorganisms usually show high thermostability, which is of great potential in industrial application; to understand the structural logic of these enzymes is helpful for the construction of robust biocatalysts. In this study, based on the crystal structure of an N-demethylase─TrSOX─with outstanding thermostability from Thermomicrobium roseum, substitutions were introduced on the aggregation interface and rigid spots to reduce the aggregation ratio and the rigidity. Four substitutions on the aggregation interface─V162S, M308S, F170S, and V306S─considerably reduced the thermostability and slightly enhanced the catalytic efficiency. In addition, the thermostable framework was considerably disrupted in several multiple P → G substitutions in several local motifs (P129G/P134G, P237G/P259G, and P259G/P276G). These structural fluctuations were in good accordance with whole-structure or partial root-mean-square deviation, radius of gyration H-bonds, and solvent-accessible surface area values in molecular dynamics simulation. Furthermore, these key spots were introduced into an unstable homolog from Bacillus sp., resulting in a dramatical increase in the half-life at 60 °C from <10 to 1440 min. These results could help understand the natural stable framework of thermophilic enzymes, which could be references for the construction of robust enzymes in industrial applications.

Multi-Objective Taguchi Optimization of Cement Concrete Incorporating Recycled Mixed Plastic Fine Aggregate Using Modified Fuller’s Equation

Motivated by the multiple benefits of recycling plastic ingredients in cementitious materials, the present study focuses on the design of sustainable cement concrete incorporating recycled mixed plastic fine aggregate (MPFA) as a partial replacement of natural sand (NS). The MPFA produced in this work is composed of a combination of polymer types with similar concoctions to those observed in the postconsumer waste streams. This study approach is vastly different from past reported studies on the use of sorted, highly purified single-type recycled plastic aggregate in cement concrete. A multi-criteria decision-making technique, Best-Worst Method (BWM), was integrated with the Taguchi method to maximize the quality of MPFA concrete based on the Fuller–Thompson theory. More specifically, an L9 (34) Taguchi orthogonal array with four three-level design factors was adopted to optimize the fresh, durability, and mechanical properties of MPFA concrete. The results showed that MPFA concrete produced with 400 kg/m3 cement content, 0.43 water/cement ratio, 0.43 fine aggregate/total aggregate ratio, and 10 vol% MPFA content exhibited the highest quality. Findings from the present work also revealed that MPFA concrete produced with tailored particle size distribution of MPFA NS fine aggregate system achieved superior, if not comparable, qualities to those of conventional concrete.

Resilience and successional trends of woody vegetation in seasonally dry tropical forests

Abstract Understanding the recovery time of vegetation structure and species composition to estimate the resilience of seasonally deciduous tropical forest (SDTF) is fundamental for conservation actions. Related information is still scarce for the semi-arid Brazilian SDTF (locally called Caatinga), which covers more than 800 000 km2 in the northeast of Brazil. We aimed to estimate how long it takes for 11 attributes of vegetation structure and species composition, separately and aggregated, to become similar to an old-growth forest (OGF). The attributes were floristic composition, species richness, Shannon diversity index, plant density, median and maximal diameters and height, basal area, volume and aboveground biomass. The attributes’ regeneration ratios were aggregated as an arithmetic average and a geometric average, based on a variance–covariance analysis. The ratios were determined in chronosequences (5, 15, 25 and 35 regeneration years and an OGF) of SDTF, in three different locations in Ceará state. Plant density, which had a unimodal tendency, reached a peak at 15 years and then decreased, although it was still greater than that of the OGF after 35 years. Richness and diversity, with monotonic trends, reached values similar to the OGF. All other attributes, especially floristic composition, volume and biomass, had lower values than the OGF. Based on the aggregate set of attributes, the SDTF was 79 per cent recovered after 35 years of regeneration. The variance–covariance analysis indicated that species richness and aboveground biomass contributed the most to the aggregate ratio of regeneration, while maximum diameter and basal area contributed the least. Recovery of this semi-arid forest takes longer than recovery of other SDTF and requires more than 35 years of regeneration to return to a composition and structure similar to the original one. Therefore, management plans should restrict destructive uses before at least 35 years of regeneration have been reached.

Developing 3D printable and buildable limestone calcined clay-based cement composites with higher aggregate content

The study investigates the effect of increasing aggregate volume on the buildability of printable mixes having ordinary Portland cement and limestone calcined clay, and aggregate-to-binder ratio of 1.5 to 3 (by weight). The experimental program is planned considering the evaluation of extrudability requirements, open time, and buildability requirements (layer compression) while printing. The effect of water-to-binder and aggregate-to-binder ratio on flowability is analysed and the dosage of superplasticizer required to attain 200 mm and 180 mm spread is determined. Further, squeeze flow and step load tests are performed to analyse the compressive resistance of the mix at different time intervals in the fresh state, while compressive strength and drying shrinkage are considered to compare the mixes in the hardened state. The factors of energy consumption and carbon emission are considered to compare the sustainability of the mixes. It is concluded that the binder-aggregate matrix governs the compression of the material in the fresh state, with the paste governing the properties in the first few minutes and then the aggregate skeleton. The compression in the fresh state is observed not to be dependent on the mix’s flowability, leading to the possibility of designing a flowable as well as buildable mix with a larger aggregate volume. Further, with an increase in the aggregate ratio from 1.5 to 3, the energy consumption of the mix reduces from 3571 to 2426 MJ and carbon dioxide emission from 462 to 314 kg CO2 for each m3 of concrete. Hence, it is concluded that a sustainable 3D printable mix with a higher aggregate-to-binder ratio can be designed while satisfying the functional needs of the concrete.

Effect of Aggregate on the Performance of Fly-Ash-Based Geopolymer Concrete

The influence of geopolymer binder characteristics on the performance of geopolymer concrete has been extensively investigated. Yet, the influence of aggregate properties has not been thoroughly studied, and it is usually assumed that their effect is the same as in cement concrete. This study investigates the effect of aggregate on the performance of fly-ash-based geopolymer concrete. A systematic experimental study was undertaken to investigate the effect of aggregate parameters, including volume fractions (AVFs), coarse aggregate to the total aggregate ratio (CAR), maximum coarse aggregate size (MAS), and fineness modulus of fine aggregate (FFM) on the compressive strength, slump, apparent volume of permeable pores (AVPPs), and the air content of geopolymer concrete. Response surface methodology (RSM) using the central composite design approach was utilized to design the experiments and analyze the results statistically. The analysis shows that all of the investigated aggregate parameters have significant first-order effects on the measured properties. No significant interaction between any of the investigated parameters was found. The aggregate may alter the geopolymerization processes, whereby SEM-EDS analysis revealed statistically significant variations in the elemental concentrations of the produced paste as the aggregate parameters changed. Quantitative weights were assigned to the effect of the investigated aggregate parameters on the measured properties. Multi-objective optimization was carried out to obtain the best combinations of the investigated parameters. Additionally, the developed contour graphs may provide an effective tool that can be used as a guide in establishing the first trial mixtures. A wide range of consistencies (10–210 mm slump) and compressive strengths (15–55 MPa) can be obtained by controlling the aggregate grading and proportions.

Combined effect of using steel fibers and demolition waste aggregates on the performance of fly ash/slag based geopolymer concrete

Developing sustainable construction products has been showing a rising trend recently. Geopolymer composites are remarkable binding materials fabricated based on recycling and sustainability. In this paper, an experimental investigation was conducted to study some mechanical and durability characteristics of steel fiber-reinforced fly ash/slag-based geopolymer concrete (GPC) with different proportions of recycled coarse aggregate. Steel fiber-reinforced geopolymer concrete mixtures incorporating recycled coarse aggregates of up to 40% at the interval of 10% were prepared, and the mixtures without recycled coarse aggregate were used as reference samples. The steel fiber ratio of 0.3% and 0.6% were used and the combined effect of steel fiber and recycled coarse aggregate on the geopolymer composites’ behavior regarding strength properties, sulfate resistance, elevated temperature resistance, abrasion resistance, and freezing-thawing resistance was addressed. A significant improvement in strength properties was observed in steel fiber reinforced recycled aggregate geopolymer concrete with increasing fiber content; however, the strength properties of geopolymer concrete were decreased with the increase of recycled coarse aggregate amount. Also, the properties such as abrasion resistance, resistance to elevated temperature, sulfate resistance, and freeze-thaw resistance were improved with the addition of steel fiber. It indicates that the synergetic effect of steel fiber and recycled aggregate helps to produce ecologically sound geopolymer concrete with good engineering properties and durability characteristics that will bring sustainability to the concrete sector. Generally, the results show that the recycled coarse aggregate ratio of up to 30% and 0.6% of steel fiber can be considered an ideal combination to make geopolymer concrete with better overall properties.

AI Mix Design of Fly Ash Admixed Concrete Based on Mechanical and Environmental Impact Considerations

It has become very important in the field of concrete technology to develop intelligent models to reduce overdependence on laboratory studies prior to concrete infrastructure designs. In order to achieve this, a database representing the global behavior and performance of concrete mixes is collected and prepared for use. In this research work, an extensive literature search was used to collect 112 concrete mixes corresponding to fly ash and binder ratios (FA/B), coarse aggregate and binder ratios (CAg/B), fine aggregate and binder ratios (FAg/B), 28-day concrete compressive strength (Fc28), and the environmental impact point (P) estimated as a life cycle assessment of greenhouse gas emissions from fly ash- and cement-based concrete. Statistical analysis, linear regression (LNR), and artificial intelligence (AI) studies were conducted on the collected database. The material binder ratios were deployed as input variables to predict Fc28 and P as the response variables. From the collected concrete mix data, it was observed that mixes with a higher cement content produce higher compressive strengths and a higher carbon footprint impact compared to mixes with a lower amount of FA. The results of the LNR and AI modeling showed that LNR performed lower than the AI techniques, with an R2(SSE) of 48.1% (26.5) for Fc and 91.2% (7.9) for P. But ANN, with performance indices of 95.5% (9.4) and 99.1% (2.6) for Fc and P, respectively, outclassed EPR with 90.3% (13.9) and 97.7% (4.2) performance indices for Fc and P, respectively. Taylor’s and variance diagrams were also used to study the behavior of the models for Fc28 and P compared to the measured values. The results show that the ANN and EPR models for Fc28 lie within the RMSE envelop of less than 0.5% and a standard deviation of between 15 MPa and 20 MPa, while the coefficient of determination sector lies between 95% and 99% except for LNR, which lies in the region of less than 80%. In the case of the P models, all the predicted models lie within the RMSE envelop of between 0.5% and 1.0%, a coefficient of determination sector of 95% and above, and a standard deviation between 2.0 and 3.0 points of impact. The variance between measured and modeled values shows that ANN has the best distribution, which agrees with the performance accuracy and fits. Lastly, the ANN learning ability was used to develop a mix design tool used to design sustainable concrete Fc28 based on environmental impact considerations. Doi: 10.28991/CEJ-SP2023-09-03 Full Text: PDF

Comparison of various machine learning algorithms used for compressive strength prediction of steel fiber-reinforced concrete

Adding hooked industrial steel fibers (ISF) to concrete boosts its tensile and flexural strength. However, the understanding of ISF’s influence on the compressive strength (CS) behavior of concrete is still questioned by the scientific society. The presented paper aims to use machine learning (ML) and deep learning (DL) algorithms to predict the CS of steel fiber reinforced concrete (SFRC) incorporating hooked ISF based on the data collected from the open literature. Accordingly, 176 sets of data are collected from different journals and conference papers. Based upon the initial sensitivity analysis, the most influential parameters like water-to-cement (W/C) ratio and content of fine aggregates (FA) tend to decrease the CS of SFRC. Meanwhile, the CS of SFRC could be enhanced by increasing the amount of superplasticizer (SP), fly ash, and cement (C). The least contributing factors include the maximum size of aggregates (Dmax) and the length-to-diameter ratio of hooked ISFs (L/DISF). Several statistical parameters are also used as metrics to evaluate the performance of implemented models, such as coefficient of determination (R2), mean absolute error (MAE), and mean of squared error (MSE). Among different ML algorithms, convolutional neural network (CNN) with R2 = 0.928, RMSE = 5.043, and MAE = 3.833 shows higher accuracy. On the other hand, K-nearest neighbor (KNN) algorithm with R2 = 0.881, RMSE = 6.477, and MAE = 4.648 results in the weakest performance.

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.

THE MONETARY COMPONENT IN ENSURING THE FINANCIAL SECURITY OF THE STATE

The paper studies the place and degree of the monetary component's influence on the level of financial security of the state in the conditions of political and socio-economic imbalances in the development of Ukraine. The aim of the research is to investigate the effectiveness of monetary policy instruments, to determine the level of the monetary component's impact on the financial security of the state, as well as to form perspectives for balancing the symbiosis of "monetary policy and national financial security". Based on the conducted research, it is established that in recent years the role of the financial security system formation at all levels has significantly increased, whether it is macroeconomic security, the security of economical subjects, or the financial security of a household. At the same time, the monetary component plays a significant role in ensuring the financial security of the state, namely, it affects macroeconomic processes in the country. Therefore, in order to ensure macroeconomic stability and economic growth in the context of ensuring the financial security of Ukraine under martial law, it is necessary to improve the mechanisms of monetary policy. The article analyzes the latest threats that lead to the negative impact of the monetary component on the financial security of the state. These include: the consequences of russian military aggression on the economic development of Ukraine, continued COVID-19 outbreaks, the introduction of administrative restrictions on the use of monetary policy instruments by the National bank of Ukraine, violations of the economic security of financial institutions, an insufficient level of financial inclusion, and the contradictory nature of the coordination of monetary and fiscal policies. In the context of establishing the decisive role of the monetary component in ensuring the financial security of the state, the adopted development strategies at the level of national security of Ukraine and at the level of the monetary sector of Ukraine are considered and systematized. The block diagram of the implementation of monetary policy in the context of ensuring the financial security of the state is proposed. It is proved that the mechanism of such interrelationship is implemented through the instruments and methods of monetary policy in combination with key macroeconomic indicators. To confirm the proposed hypothesis, the econometric model of the influence of monetary instruments on the level of financial security of the state is developed. As a proxy indicator of the financial security of Ukraine, the Financial Stress Index is used, which reflects the current state of the financial sector (without considering future risks) and consists of sub-indices for the banking sector, households, government and corporate securities, and foreign exchange market. Estimated and re-estimated models made it possible to determine the most influential indicators of the monetary component of the Financial Stress Index, namely: consumer price index; producer price index; GDP to monetary aggregate M2 ratio; cash to GDP ratio; share of foreign currency in monetary aggregate M3; NBU key policy rate (annual average); share of non-performing loans (NPL). The proposed model can be used to forecast the influence of the parameters of the monetary component on the level of financial security of the state.Based on the results of the study, it is proved that, despite the difficult political and economic situation in Ukraine, it is necessary to focus on improving the coordination of monetary and fiscal policies, considering the further implementation of the main provisions of international documents adopted by International Monetary Fund on this issue.

Improvement of fresh and hardened properties of a sustainable HFRSCC using various powders as multi-blended binders

Hybrid fiber-reinforced self-compacting concrete (HFRSCC) has been very popular in recent years due to its high mechanical, durability and flexural performance. HFRSCC properties are also closely related to its workability properties. Therefore, a high proportion of binder material is required to provide a uniform distribution of the fibers in the matrix. The use of mineral admixtures replaced by cement has a vital importance to improve especially the workability of HFRSCC mixtures, resulting in reduction of CO2 emission because the production of 1 ton Portland cement releases about 1 ton of CO2. For this reason, in this study, the effects of multi-blended (binary, ternary and quaternary) binders containing Portland Cement (PC), fly ash (FA), ground granulated blast furnace slag (BS) and limestone powder (LP) on the workability (Slump-flow, T500, J-ring and V-funnel) and hardened (compressive, splitting tensile and flexural tensile strength) properties of HFRSCC as well as flexural performance for 7, 28 and 90 days are investigated. The first of three group mixtures in this study consists of only control mixture (Control) without fiber and mineral admixture blends (MAB), in second group there are four SCC mixtures with only MAB replaced by cement as binary, ternary, quaternary SCC-MAB and the last group also includes four SCC mixtures with both mineral admixtures same as second group and hybrid fiber (HFRSCC-MAB). The total binder amount, water/binder ratio, fine aggregate/all aggregate ratio and fiber hybridization are kept constant while the mineral admixture type and blending system are variable parameters. According to the test results, among the HFRSCC-MAB blends, the quaternary blend system performed the best in terms of workability, followed by the binary blends containing FA. In addition, when it came to ultimate strengths, hybrid fiber-reinforced samples with ternary blends performed best for compressive strength, while hybrid fiber-reinforced samples with binary blends containing FA performed best for splitting tensile and flexural tensile strengths. Finally, it has been seen that the use of various powders as multi-blended binders is a successful solution to obtain high workability for uniform distribution of fibers in HFRSCC as well as high compressive strength and flexural performance, resulting in economical, eco-friendly and sustainable composite.

Long-term performance of steel-spontaneous combustion coal gangue aggregate concrete composite slabs considering the influence of non-uniform shrinkage

The long-term performance of steel-spontaneous combustion coal gangue aggregate concrete (S-SCGAC) composite slabs was investigated in this study. Shrinkage tests were performed on 20 groups of specimens to quantify the effects of the replacement ratio (rc) of spontaneous-combustion coal gangue aggregate (SCGA) and humidity boundary conditions on the shrinkage of SCGAC specimens. A non-uniform shrinkage model for S-SCGAC composite slabs was further proposed. A long-term performance design method of S-SCGAC composite slabs was put forward by using ABAQUS software to establish a finite element model of the long-term performance of composite slabs considering the influence of non-uniform shrinkage, and to quantify the influence of parameters on the long-term performance. The results showed that the shrinkage deformation of SCGAC specimens increased significantly with increasing rc, and humidity boundary conditions were found to have a significant effect on the shrinkage performance of SCGAC specimens. The exposed surface shrinkage of the concrete under single-sided humidity transfer conditions was 1.01–1.09 times that under double-sided humidity transfer conditions, and the sealed surface shrinkage of the concrete under single-sided humidity transfer conditions was only 5.4%–14.4% of that under double-sided humidity transfer conditions. The long-term deflection of S-SCGAC composite slabs proved to be significantly affected by rc. When rc increased from 0% to 100%, the long-term deflection of the composite slab increased on average by 67.2%. The long-term deflection calculation method considering the effect of non-uniform shrinkage was shown to yield promising prediction results.

Multiscale investigation of self-consolidating earthen materials using a novel concrete-equivalent mortar approach

Earth-based materials have been used since ancient times due to their low environmental impact and superior thermal performance. The rammed earth (RE) method, as a common earthen construction, consists in casting the material layer-by-layer, which is time-consuming, labor-intensive, and energy consuming. Designing self-consolidating earth concrete (SCEC) can speed up the construction process and overcome the disadvantages of conventional RE and enhance its performance. Achieving high fluidity and adequate compressive strength for early demolding is challenging because of the presence of clay and low cement content, respectively. Moreover, diversity of existing soil types does not allow to propose a universal mixture proportioning approach. In this study, workability, drying shrinkage, and compressive strength of SCEC mixtures were evaluated using a new concrete-equivalent mortar (CEM) approach to facilitate the optimization process and reduce the number of experiments and materials. The approach is mainly based on optimizing the excess paste (EP) thickness to consider the variation of packing density of the granular skeleton. The mixture parameters included the water-to-powder ratio (W/P), volumetric sand-to-total aggregate ratio (S/A), and the excess paste thickness. Good correlations between the investigated CEMs and their corresponding concrete mixtures were established. According to the carried-out ANOVA analysis, the main influencing parameters on workability, drying shrinkage, and compressive strength of SCEC include the specific surface area and Atterberg limits of the ternary binder system, W/P, paste volume, and EP thickness.

Physical and mechanical properties of foamed concrete with recycled concrete aggregates

A large amount of waste concrete is produced during old city reconstruction. In order to realize the lightweight reuse of recycled concrete aggregate, a new preparation scheme of foamed concrete is proposed. Through single-factor tests, the effects of recycled coarse aggregate (RCA) gradation, RCA volume ratio, water-cement ratio and foam content on the preparation process and performance of RCA foamed concrete (RCAFC) were explored. The results showed that RCA grade has significant influence on the performance of RCAFC. Grading level Ⅲ (i.e., the mass ratio of five-type aggregates sized, respectively, 9.5–16 mm, 16–19 mm, 19–26.5 mm, 26.5–31.5 mm and 31.5–37.5 mm is 2:4:8:3:3) can reduce the water absorption by 4.6%, increase the compressive strength by 6.0%, and decrease the difficulty of sample preparation compared with the natural grading. The increase of RCA volume fraction is directly proportional to the compressive strength and inversely proportional to the water absorption. With the raising of water-cement ratio, the fluidity of foamed concrete paste increases linearly, the dry density decreases, the water absorption decreases first and then increases, and the compressive strength increases first and then decreases. The increase of foam content is inversely proportional to fluidity, dry density and compressive strength, and it is directly proportional to water absorption. Among the above four factors, the grade of RCA has the greatest impact on the early strength of the sample, whilst the content of foam is the smallest.

Effect of fine aggregate on fluidity and mechanical properties of wet shotcrete

Air-entrained wet shotcrete improves the pipeline transportation efficiency of concrete. The characteristics of the fine aggregate in the mix have different effects on the fluidity and mechanical properties of air-entrained wet shotcrete. The effects of four different properties of fine aggregates (mud content, sand ratio, water content and particle size) on the fluidity and mechanical properties of air-entrained wet shotcrete were studied, with particular attention paid to the sand ratio and mud content. The fluidity and mechanical properties of wet shotcrete were optimum when the sand ratio of the fine aggregate was 0.56 and the water content was 3%. The fine aggregate should have a reasonable particle size as far as possible. Montmorillonite in the mud inhibited the fluidity and mechanical properties, so mud content should be kept as low as possible. The results of this work provide a reference for the practical application of air-entrained wet shotcrete, so as to better deal with pipe blockage.