Two-stage Concrete Research Articles

Forecasting the strength of preplaced aggregate concrete using interpretable machine learning approaches

Preplaced aggregate concrete (PAC) also known as two-stage concrete (TSC) is widely used in construction engineering for various applications. To produce PAC, a mixture of Portland cement, sand, and admixtures is injected into a mold subsequent to the deposition of coarse aggregate. This process complicates the prediction of compressive strength (CS), demanding thorough investigation. Consequently, the emphasis of this study is on enhancing the comprehension of PAC compressive strength using machine learning models. Thirteen models are evaluated with 261 data points and eleven input variables. The result depicts that xgboost demonstrates exceptional accuracy with a correlation coefficient of 0.9791 and a normalized coefficient of determination (R2) of 0.9583. Moreover, Gradient boosting (GB) and Cat boost (CB) also perform well due to its robust performance. In addition, Adaboost, Voting regressor, and Random forest yield precise predictions with low mean absolute error (MAE) and root mean square error (RMSE) values. The sensitivity analysis (SA) reveals the significant impact of key input parameters on overall model sensitivity. Notably, gravel takes the lead with a substantial 44.7% contribution, followed by sand at 19.5%, cement at 15.6%, and Fly ash and GGBS at 5.9% and 5.1%, respectively. The best fit model i.e., XG-Boost model, was employed for SHAP analysis to assess the relative importance of contributing attributes and optimize input variables. The SHAP analysis unveiled the water-to-binder (W/B) ratio, superplasticizer, and gravel as the most significant factors influencing the CS of PAC. Furthermore, graphical user interface (GUI) have been developed for practical applications in predicting concrete strength. This simplifies the process and offers a valuable tool for leveraging the model's potential in the field of civil engineering. This comprehensive evaluation provides valuable insights to researchers and practitioners, empowering them to make informed choices in predicting PAC compressive strength in construction projects. By enhancing the reliability and applicability of predictive models, this study contributes to the field of preplaced aggregate concrete strength prediction.

Effects of the shape, size, and surface roughness of glass coarse aggregate on the mechanical properties of two-stage concrete

Because two-stage concrete (TSC) is obtained by placing coarse aggregate in formwork and then filling the gaps with flowable grout, the properties of the coarse aggregate can notably affect the mechanical properties of TSC. In this study, uniaxial compressive and splitting tensile tests were conducted on TSC with eleven types of glass coarse aggregate of different shapes, sizes, and surface roughness for coarse aggregate. Two types of spherical glass aggregate with diameters of 17 and 30 mm, irregular shape of crushed glass plate classified into two size groups (20–30 mm and 10–20 mm) were used. Surfaces of spherical glass aggregates were two types; those were smooth and rough. The compressive strength of grout matrices used in specimens was 44.6 N/mm2 in the normal-strength mixture and 129.8 N/mm2 in the high-strength one. The relationship between the compressive and tensile strengths and the size of the coarse aggregate changed depending on the grout matrix strength and roughness of the coarse aggregate surface. The tensile strength for crushed glass aggregate were larger than those for spherical glass aggregate. Increasing roughness of the coarse aggregate surface led to an increase in the tensile and compressive strengths. The modulus of elasticity was affected by not only the solid content aggregate but also the shape and roughness. Moreover, the mechanical properties of TSC were compared with those of conventional concrete with the same coarse aggregate and same water-cement ratio as TSC. Observations from the test program indicate the design parameters that most strongly influence the strength and stiffness of TSC specimens.

Prediction of compressive strength of two-stage (preplaced aggregate) concrete using gene expression programming and random forest

The aim of this research is to predict preplaced-aggregate concrete (PAC) compressive strength (CS) by using machine learning approaches such as gene expression programming (GEP) and random forest (RF). PAC requires injecting a portland cement-sand grout with admixtures into a mold after coarse aggregate has been deposited, making CS prediction complicated and requiring substantial study. Machine learning methods were used to cut down on the time and money needed for extensive experimental testing. The database includes 135 values for CS with eleven input variables. There is an acceptable degree of agreement between predicted and experimental values, as shown by the CS R2 values of 0.94 for GEP and 0.96 for RF. When comparing RF with GEP, RF performed better as measured by R2. The lower values displayed by the statistical error also showed that RF performed better than GEP. To compare, the GEP model's COV, MAE, RSME, and RMSLE were 0.527, 1.569, 2.706, and 0.133, whereas those for RF were 0.450, 1.648, 2.17, and 0.092. The SHAP analysis showed the effects of each input parameter, illuminating the positive effect of increasing the superplasticizer content on strength and the negative effect of raising the water-to-binder ratio. Using machine learning approaches to forecast the CS of PAC, this study has the potential to boost environmental protection and economic advantage.

Optimizing ultra-high performance cementitious functionally graded composite slab towards bullet impact resistance

This study develops functionally graded composite slab (FGCS) by a one-time grouting approach based on the design concepts of ultra-high performance fibre reinforced concrete (UHPFRC) and two-stage concrete (TSC). The anti-penetration performance of the FGCS targets is investigated against 7.62 mm in-service bullets with shooting velocity of 843 m/s. The results show that while the TSC target presents superior bullet penetration resistance, it concurrently poses a significant threat of widespread cracking damage. Upon weighing the factors of bullet penetration and risk of cracking, the FGCS emerges as a more viable candidate for protective structures. The FGCS target is cast through a one-time grouting method, and there is no interface delamination under the projectile impact. The optimized FGCS exhibits enhanced in-service bullet impact resistance and a reduced safety thickness of 80 mm compared to the normal UHPFRC.

Engineering properties of two-stage concrete: A critical review

Conventional Concrete (CC) is a highly used material in construction industries. CC has certain advantages and disadvantages depending on materials, material proportions, and method of preparation. Flaws like lesser sustainability and higher cost of production create the necessity of research to find an alternative solution. Two-Stage Concrete (TSC), also known as Preplaced Aggregate Concrete (PAC), which is similar to the CC on the basis of its constituent materials. However, it is produced using a unique procedure that differs from conventional concrete. Production of Two-Stage concrete is done in two stages. Initially, coarse aggregates are filled in a tight formwork or mold and then voids between the aggregates are filled by injecting cementitious grout. This unique placement technique changes the load-transfer mechanism in TSC, leading to improved mechanical properties.This paper critically reviews the TSC, including its history of development, engineering properties, long term performance, and construction methods that enhance the understanding of its behavior, thus paving the way for wider implementation of TSC in today’s construction industry. From the study, several conclusions are drawn and it is seen that TSC is used in the construction of Nuclear Power-Plants and Bio-chemical storage plants to minimize segregation problems. TSC makes construction cost-effective due to the higher percentage of coarser particles and improves mechanical properties with partial replacement of constituents without affecting its strength.

Laboratory Investigation into the Flexural Behavior of Embedded Concrete Sleepers in Two-Stage Concrete with Preplaced Ballast Aggregate

The conversion of ballasted railway tracks into slab tracks using the preplaced aggregate concrete (PAC) technology over the bridges and in the tunnels has been introduced by many researchers but the flexural behavior of this composite system has not yet been studied. Therefore, in the first stage, a series of mortar and concrete mixture designs were proposed and evaluated. Subsequently, a concrete beam mold with dimensions of 3 * 0.6 * 0.5 m, which represented the track conditions, was developed and the bending behavior of the constructed beams in both conditions of the presence and absence of the concert B70 sleeper were investigated. The maximum bending force in the middle of the concrete beam without a sleeper (SE) equaled 177.5 kN. In addition, the average values of bending tolerance by the sleeper including a PAC beam for three specimens in the four modes of the positive moment of midspan (SPM), negative moment of midspan (SNM), positive moment of rail seat (SPR), and negative moment of rail seat (SNR) were 55.25 kN m, 32.5 kN m, 91.84 kN m, and 38.21 kN m, respectively, which met the requirements of the AREMA regulations.

Effect of slag coal ash and foamed glass on the mechanical properties of two-stage concrete

Two-stage concrete (TSC) is known by various names such as colcrete, Polcrete, preplaced aggregate concrete and prepacked concrete. It is different from traditional concrete in two fundamental ways, namely method of construction and mix proportion. Two-stage concrete (TSC) is defined as firstly, coarse aggregates are placed into the formwork and grout is applied to fill in the between coarse aggregate particles voids. Secondly, the percentage of coarse aggregates in the mix proportion of TSC is higher than that in normal concrete. The typical value is about 60% as compared with 40% in traditional concrete. As coarse aggregates are preplaced first, they can occupy up to 60–70% of the total volume. As coarse aggregates are not involved in the mixing process, TSC is environmentally friendly with lesser consumption of energy. With a higher content of aggregates, TSC reduces the use of cement by 20–30% and may minimize the temperature rise. Engineering properties of TSC, including its stress–strain relationship, is mainly governed by the properties of coarse aggregates as stress is transferred from the skeleton of aggregates to hardened grout. Main advantages of TSC include a higher volume of coarse aggregates and the ability to use larger size coarse aggregates. The latter also reduces the cost of crushing. TSC has beneficial properties such as low drying shrinkage, high bonding strength, high modulus of elasticity, and excellent durability. The method of TSC has proved particularly useful in a number of applications like underwater construction, and masonry repair, where placement by conventional methods is extremely difficult. The method is also applicable in case of massive concrete where low heat of hydration is required. It is studied the feasibility of casting two stage concrete with 100% steel slag as coarse aggregate. In term of formulation, to adopt two stage concreting method we could minimize the risk of concrete bleeding and segregation due to high water absorption and quite high density of slag aggregate. The effect of slag coal ash and foamed glass on the mechanical properties of two-stage concrete has rarely been reported. Thus, the development of an eco-efficient alkali-activated grout for two-stage concrete is a new research topic that has no robust results to draw solid conclusions and it should blaze the track towards a cleaner production of building materials with outstanding sustainability.

Effect of Recycled Coarse Aggregate and Bagasse Ash on Two-Stage Concrete

Numerous research studies have been conducted to improve the weak properties of recycled aggregate as a construction material over the last few decades. In two-stage concrete (TSC), coarse aggregates are placed in formwork, and then grout is injected with high pressure to fill up the voids between the coarse aggregates. In this experimental research, TSC was made with 100% recycled coarse aggregate (RCA). Ten percent and twenty percent bagasse ash was used as a fractional substitution of cement along with the RCA. Conventional concrete with 100% natural coarse aggregate (NCA) and 100% RCA was made to determine compressive strength only. Compressive strength reduction in the TSC was 14.36% when 100% RCA was used. Tensile strength in the TSC decreased when 100% RCA was used. The increase in compressive strength was 8.47% when 20% bagasse ash was used compared to the TSC mix that had 100% RCA. The compressive strength of the TSC at 250 °C was also determined to find the reduction in strength at high temperature. Moreover, the compressive and tensile strength of the TSC that had RCA was improved by the addition of bagasse ash.

Sustainable Use of Waste Polypropylene Fibres to Enhance the Abrasion and Skid Resistance of Two-Stage Concrete

Two-stage concrete (TSC), also known as prepacked aggregate concrete (PAC), differs from traditional concrete in terms of site application and manufacturing process. Although this type of concrete is not a replacement for conventional concrete applications, it is an ideal option for unusual and difficult placing conditions, especially for repairing existing concrete structures. In other words, this type of concrete is a newly developed concrete and made by placing and packing coarse aggregates and fibres in a designed formwork, then injecting a cement grout mixture into the free spaces between the aggregate particles using gravity or a pump device. For the mentioned system and others, concrete components used as floors or pavements must have an adequate degree of roughness during service life when exposed to skid and abrasion. Thus, this research work introduced a new concrete method (prepacked aggregates fibre-reinforced concrete—PAFRC) with high abrasion and skid resistance reinforced with waste polypropylene (PP) fibres from the carpet industry. The effects of PP fibres at 0–1% dosages on the mechanical properties, abrasion resistance, and skid resistance of PAFRC mixes were studied. The results revealed that the addition of PP fibres reduces the compressive strength of concrete mixtures. Nonetheless, the presence of PP fibres results in PAFRC mixes having higher tensile strength, abrasion resistance, and skid resistance than plain concrete. It was detected that in both grouting methods (gravity and pump), with the addition of PP fibre up to a specific dosage, the resistance against abrasion and skid was increased by about 26% compared to plain PAC mix. Additionally, the outcomes indicated that PAFRC is a promising material for applications such as pavements with high abrasion and skid resistance.

Research on flexure and impact performance of functionally-graded two-stage fibrous concrete beams of different sizes

This research focuses on developing functionally-graded two-stage fibrous concrete (FGTFC) comprising steel and polypropylene fibres to enhance impact resistance and alleviate the damage. The FGTFC was developed based on the bionic-inspired impact resistance of turtle shells. This research examines the flexural and impact performance of FGTFC beams of three sizes. Three different beams were prepared of size 250 × 50 × 50 mm, 400 × 100 × 100 mm and 550 × 150 × 150 mm with a 2.4% average dosage of steel and polypropylene fibres. Additionally, steel and polypropylene used in this study are the new types of fibres which are not used by researchers and not found in the literature. Totally twelve mixtures were prepared; one was Two-Stage Concrete (TSC) and considered a reference specimen. Two-Stage Fibrous Concrete (TSFC) was another two with fully reinforced single layer cross-sectional beams, with their fibres constituents being dispersed evenly. The remaining were two and three-layered FGTFC beams with evenly dispersed fibre constituents. Uneven dispersion in the current research meant that the fibre dosage was more in the peripheral layers and less in the inner layers, despite the fibre dosage being used remains the same in all beams. The fabricated FGTFC beams were synchronously cast using cement grout and tested against the three-point bending and falling mass impact. All beams were tested through the falling mass impact as per the guidelines of ACI Committee 544. Compressive strength, first crack and peak stress, flexural toughness, initial crack impact number, failure impact number, impact ductility index, and failure patterns were examined. Findings indicated that the peak load, flexural toughness and impact strength increased significantly with increased beam size. Additionally, steel fibre significantly contributed to increasing flexural toughness and impact strength than the polypropylene fibre. Thus, the proposed three-layer FGTFC beams had greater efficacy and exceptional fiber usage in the peripheral layers, despite the exact fibre dosage in all TSFC beams.

Static and Dynamic Performance of Two Stage Concrete

Concrete is arguably the most important construction material in the world. In the last decades, it has been reported that infrastructures faced extreme static and dynamic loads which caused structural catastrophic disasters [1]. The increase usage of conventional concrete in engineering industries led to high consumption of mineral resources which caused several environmental damages related to reduction in the rocket layers [2], besides, the economical damages due to the high demand of natural resources materials which rises the cost of construction [3]. Therefore, the utilization of recycled waste rubber (steel wires) in concrete can be a sustainable solution for waste construction developments [4]. Recently, two stage concrete (TSC) (non-traditional concrete) was introduced. Placing of coarse aggregate followed by injecting the cementitious materials among the aggregate layers in the formwork are the basic steps of producing TSC. Evaluating the static and dynamic performance of TSC were the objectives of this study. Cement, aggregates, water, recycled steel wires of rubber tires were utilized in manufacturing TSC specimens. The compressive characteristic and impact resistance of TSC test specimens were evaluated. Results showed that steel wires improved the dynamic behaviour of TSC, while a slight to no effect was observed on its compressive characteristics. This study demonstrates the potential to engineer sustainable TSC mixtures.

Blast-resistant performance of a two-stage concrete plate subjected to contact explosions

Threats posed by explosions due to terrorism or industrial accidents should be considered in the structural design of infrastructure and other valuable facilities. Protective structures, such as perimeter concrete walls, are effective at reducing explosive damage. Although two-stage concrete (TSC) has some advantages over conventional concrete in constructing such protective structures, studies concerning the behavior of TSC subjected to blast loads are very limited. In the current study, the effects of TSC strength, maximum diameter of coarse aggregate, and type of coarse aggregate are examined experimentally to determine how these parameters affect the local failure of a TSC plate subjected to contact explosion. For various TSC strengths and properties of coarse aggregate, critical values of spall occurrence as a function of plate thickness and charge mass are provided, and prediction equations of local failure depth are provided.

Evaluation of Mechanical Properties of Two-Stage Concrete and Conventional Concrete Using Nondestructive Tests

AbstractDifferent types of concrete mixtures are used as building materials. The manufacturing process of two-stage concrete (TSC) differs from that of conventional concrete. This study investigate...

Functionally graded ultra-high performance cementitious composite with enhanced impact properties

This study develops functionally graded ultra-high performance cementitious composite beams by applying the composite concepts of Ultra-high Performance Concrete (UHPC), Two-stage Concrete (TSC) and Slurry-infiltrated Fibrous Concrete (SIFCON). The functionally graded composite beam (FGCB) is fabricated with a bottom layer of SIFCON and top layer of TSC, and the two layers are synchronously cast by using UHPC slurry. The novel concept of FGCB is proposed towards more economical and high performance structural systems, namely excellent flexural bearing capacity and impact resistance, low cement consumption and high steel fibre utilization efficiency. The fresh and hardened properties of UHPC slurry, flexural and impact properties of FGCB are measured. The results reveal that the designed FGCB has superior flexural properties and impact resistance, without showing any interfacial bond problem. The fibre utilization efficiency of the designed FGCB is very high compared to the traditional UHPC and SIFCON beams. The 30 mm medium hook-ended steel fibres show the best utilization efficiency compared to the 13 mm short straight and 60 mm long 5D steel fibres, and 3% medium fibres are optimum to design FGCB. The low-velocity impact resistance of FGCB is well linearly correlated with its static flexural toughness.

RETRACTED: Enhancement of strength and transport properties of a novel preplaced aggregate fiber reinforced concrete by adding waste polypropylene carpet fibers

Preplaced aggregate concrete (PAC), also known as two-stage concrete (TSC), is a particular type of concrete that is produced by placing coarse aggregates in a form and voids amongst them are then injected with a flowable grout. The preplaced aggregate fiber reinforced concrete (PAFRC) is new developed concrete, with a unique mixture of coarse aggregates and short fibers that are premixed and preplaced in the formwork and injecting grout into the voids of the aggregate mass. The current study develops the concept of a new PAFRC reinforced with waste polypropylene (PP) carpet fibers and investigate its strength and transport properties. Palm oil fuel ash (POFA) was used as partial cement replacement. Six PAFRC mixes with fibers varying from 0 to 1.25% with a length of 30 mm were made by the gravity method. Another six batches with the similar fiber dosages were made, where the pumping method was used to inject the grout into the voids between the aggregates. The results showed that by adding carpet fibers, the compressive strength of PAFRC specimens reduced. However, the PAFRC specimens revealed a notable enhancement in the tensile strength values. Moreover, water absorption, sorptivity, and chloride penetration depth were reduced for POFA-based PAFRC specimens reinforced with carpet fibers. The study revealed that the carpet fibers are potential to be used in PAFRC by developing the transport and strength properties.

Effect of coarse grain aggregate on strength parameters of two-stage concrete

. Two-stage concrete (TSC) is a special type of concrete that the method of its construction and implementation is different from conventional one. In TSC, coarse aggregate particles are first placed in the formwork and voids between them are subsequently injected with a special cementations mixture. TSC has been successfully used in many applications, such as underwater construction, casting concrete sections congested with reinforcement and concrete repair. Coarse aggregate forms about 60% of the total volume of TSC, while coarse aggregate forms about 40% of the total volume of conventional concrete. In TSC stresses are transferred through contact areas between coarse aggregate particles. In this paper coarse aggregate size influence on strength parameters of TSC and comparing it with conventional concrete is done (by uniaxial compressive strength test and Brazilian tensile strength test). According to results of tests in this paper, the TSC with finest grain of coarse aggregate has higher compressive and tensile strength, higher modulus of elasticity and less Poisson’s ratio from conventional concrete.

Impact Resistance and Strength Reliability of Novel Two-Stage Fibre-Reinforced Concrete

Two-stage fibre-reinforced concrete (TSFRC) is a novel fibrous concrete that differs from the conventional fibre-reinforced concrete (FRC) in several aspects including its placement technique, implementation, fabrication methodology, and high coarse aggregate content. Consequently, the available data from the open literature on the behaviour of the conventional FRC exposed to falling weight collision may not be applicable to TSFRC. For instance, the impact strength performance of the conventional FRC is well documented; however, for TSFRC this has not been duly examined. For the first time, this study pioneers the concept of impact strength of TSFRC under falling weight collision. For this purpose, short crimped fibres and long hooked end steel fibres at 1.5, 3.0, and 5.0% dosage were used in two-stage concrete (TSC). To this end, seven different mixes were prepared and tested under falling weight collision as per ACI committee 544. In addition, a statistical analysis has been performed to analyse the scattered test results by Weibull distribution. For determining Weibull parameters, 20 probability estimators have been used, and the best estimators are taken for the reliability analysis. Based on the obtained Weibull parameters, the impact strength of TSFRC has been reported in terms of reliability. The results revealed that the ability of using higher fibre dosages allows achieving greater impact resistance properties for novel manufacturing TSFRC. Indeed, the TSC with steel fibre dosages exceeding 5%, can be produced easily thus making this innovative, yet simple to produce concrete, a strong contender in many construction applications. The two-parameter Weibull theory has been found to be adequately suitable for analysing the variations in the number of impacts that induces first crack and failure of all group of TSFRC specimens.

Two-Stage Concrete as a Sustainable Production

Two-stage concrete (TSC) is a sustainable concrete which is produced by forcing a flowable cement grout mixture through the voids of a skeletal mass made of compacted preplaced aggregates. From the technical and economic aspects, TSC is particularly useful for construction and repair of concrete structures especially foundations, underwater construction, nuclear reactors, concrete dams, heritage structures and in constructions with closely spaced reinforcement. TSC differs from ordinary concrete in that it contains a higher proportion of stone aggregate and the aggregate stays in point-to-point contact as placed. Thus, the mechanical characteristics of the TSC in failure conditions are distinctly different from ordinary concrete. This paper presents the results of experimental investigations conducted to evaluate the compressive, tensile strength and modulus of elasticity of TSC using grouts with different water-to-cement ratios and admixture contents. It was found that the modulus of elasticity and splitting tensile strength of TSC are equivalent or higher than that of conventional concrete at the same compressive strength. In this method of construction, the splitting tensile strength can be conservatively estimated using the American concrete institute (ACI) equation for conventional concrete.

Two-Stage Concrete as a Sustainable Production

Two-stage concrete (TSC) is a sustainable concrete which is produced by forcing a flowable cement grout mixture through the voids of a skeletal mass made of compacted preplaced aggregates. From the technical and economic aspects, TSC is particularly useful for construction and repair of concrete structures especially foundations, underwater construction, nuclear reactors, concrete dams, heritage structures and in constructions with closely spaced reinforcement. TSC differs from ordinary concrete in that it contains a higher proportion of stone aggregate and the aggregate stays in point-to-point contact as placed. Thus, the mechanical characteristics of the TSC in failure conditions are distinctly different from ordinary concrete. This paper presents the results of experimental investigations conducted to evaluate the compressive, tensile strength and modulus of elasticity of TSC using grouts with different water-to-cement ratios and admixture contents. It was found that the modulus of elasticity and splitting tensile strength of TSC are equivalent or higher than that of conventional concrete at the same compressive strength. In this method of construction, the splitting tensile strength can be conservatively estimated using the American concrete institute (ACI) equation for conventional concrete.

Simple empirical formula to estimate the main geomechanical parameters of preplaced aggregate concrete and conventional concrete

Preplaced aggregate concrete (PAC) or two-stage concrete is a specific type of concrete successfully employed in many projects including underwater concrete structures, massive concrete structures, structures made of reinforced concrete, and improvement of concrete structures. PAC is significantly different than the conventional concrete. In this type of concrete, aggregates are initially poured into the mold, the voids between which are then filled with sand and cement mortar. Additionally, the concrete provides grain-to-grain contact for the aggregates. Since use of PAC in construction projects is growing, this paper is aimed to present experimental relations for estimation of geomechanical parameters of PAC and conventional concrete. To this end, 144 and 72 specimens made of PAC and conventional concrete, respectively, were prepared, on which uniaxial compression test, Brazilian tensile test, and point load test were conducted. Then, the resulting data from the experiments were classified into two categories, namely the regression and the test data. Moreover, experimental relations were obtained between the compressive strength, tensile strength, Young’s modulus, corrected point load index, and Poisson’s ratio for both conventional concrete and PAC, and their validity were then investigated. The results indicated that the obtained relations could be used to estimate the geomechanical properties of PAC and conventional concrete with acceptable accuracy.