Slump Loss Research Articles

Study on the properties of recycled concrete mixed with coal gangue: Mechanics, workability and microstructure

Coal gangue is a by-product in the process of coal mining. Calcined coal gangue powder and coal gangue aggregate are used to prepare concrete, which can not only enhance the utilization rate of coal gangue, but also improve the performance of coal gangue concrete. In this study, calcined coal gangue powder (CCGP) was employed as an auxiliary cementation material, and coal gangue was employed as coarse concrete aggregate (CCA). Different mix proportions were designed to prepare 180 concrete specimens, and slump, cube compressive strength, splitting tensile strength and SEM test were carried out, respectively. The results show that after standing for 120min, the slump of CP0CA0 group is 53 mm, while the slump of CP30CA0 group is only 48 mm. CCGP can reduce the slump loss of concrete over time. The incorporation of CCGP into coal gangue concrete (CGC) can improve the late strength of concrete. When the substitution rate of CCA is constant, the CGC whose substitution rate of CCGP is 20 % will have the best mechanical properties: the compressive strength values are 49.67 MPa, 39.22 MPa and 27.35 MPa; the splitting tensile strength values are 2.92 MPa, 2.59 MPa and 1.92 MPa. In addition, how CCGP affects the mechanical properties of CGC was analyzed from the microscopic level in this paper. Through the regression analysis of the test data, the conversion relationship between the compressive strength and the splitting tensile strength of the concrete mixed with CCGP and CCA was obtained, which can be used to predict the splitting tensile strength. The results of this study can provide a new research idea for the efficient utilization of coal gangue.

Effect of binder and activator composition on the characteristics of alkali-activated slag-based concrete

Alkali Activated Slag Concrete (AASC) has been a sustained research activity over the past two decades. Its promising characteristics and being environmentally friendly compared to Ordinary Portland Cement made AASC of exceptional interest. However, there is still no firm mix design, for the AASC, that can provide desirable fresh and hardened properties based on the composition of the binder and activator. This research specifically aims to investigate the affecting parameters on the slump and compressive strength of alkali-activated slag/lime-based concrete and provide a better understanding of the potential reasons for these characteristics. The experimental program consisted of two stages; the first stage studied the effect of different binder and activator compositions, and the second stage studied the water-to-binder ratio and binder content effects on the slump and compressive strength of alkali-activated slag/lime-based concrete. The binder and activator compositions were defined through two main parameters, the hybrid factor (HF = CaO/Si2O + Al2O3) and the solution modulus (Ms = SiO2/Na2O). The compressive strength, initial slump, and slump loss were measured to evaluate the different mixes and specify the optimum range of compositions. Based on the studied parameters, the effective range to achieve desirable slump and concrete compressive strength is from HF 0.6 up to 0.8 at Ms 1.5, this would achieve a compressive strength of more than 30 MPa and a slump of 100 mm after 90 min.

Extended discharge time of ready-mixed concrete: Myth or necessity?

A significant volume of pre-mixed concrete is frequently sent back to batching plants for disposal due to various factors such as excessive slump loss during transportation, overproduction, and experimentation with new batches. It is estimated that approximately 3 % of the total concrete production becomes waste. Rejecting numerous truckloads of concrete is typically based on strict adherence to the concrete discharge 90-minute time limit. This study investigates the effects of extending the discharge time on the properties of fresh and hardened ready-mixed concrete, as well as its durability. To emulate typical field construction conditions, we formulated representative concrete mixtures and sourced, batched, and poured them from a local ready-mix concrete supplier. To maintain the concrete's workability without altering the mix design, high-range water reducer (retarder or stabilizer), and air-entrainment admixtures were incorporated as needed. The fresh and hardened concrete properties were evaluated at batching and at time intervals of 60, 90, 120, and 150 minutes for three different concrete mixtures. Fresh concrete properties included air content, slump, and temperature, while hardened concrete properties encompassed compressive strength, freeze-thaw resistance, and surface resistivity. Remarkably, the discharge time had no significant impact on the fresh and hardened concrete properties even up to 150 minutes. This indicates that the strict discharge time limit is overly cautious. Embracing an extended discharge time offers numerous economic and sustainable advantages.

The influence of slag content on the mechanical properties of high-strength concrete

In light of the current situation where excessive amounts of excavated earth from subway tunnel construction are being stacked with low utilization and value, this study used residue as a mineral admixture to investigate the effects of different proportions of residue content (0%, 2.5%, 5.0%, 7.5%, and 10.0%) on the workability and mechanical properties of C50 concrete. The results indicate that: (1) The initial slump and slump loss of C50 concrete decrease gradually as the residue content increases. (2) The compressive strength of C50 concrete with varying residue contents is lower than the control group at early stages (3d, 7d), while it is higher than the control group at 28d. There exists an optimal content of residue for improving C50 concrete compressive strength, and it is found that the highest compressive strength at 28d is achieved when the residue content is 7.5% of the cement content. (3) The microscopic structure of C50 concrete with different residue contents at 28d shows that as the residue content increases, the microscopic structure of C50 concrete gradually becomes more compact and the porosity decreases.

Development of Sustainable Slag-based Geopolymer Concrete Using Different Types of Chemical Admixtures

Geopolymer concrete (GPC) has achieved a wide popularity since innovating it as an alternative to conventional concrete because of its superior mechanical characteristics and durability, in addition to being a green concrete due to its low negative impact on the environment. However, GPC still suffers from the problem of its poor workability which suppresses its spread in construction applications. This study investigated the most effective parameters on the workability of GPC including GGBFS content, water to binder ratio, and dosage of different types of chemical admixtures, Naphthalene-Based Admixture (NPA) and Polycarboxylate-Based Admixture (PCA), using Taguchi approach and Analysis of Variance (ANOVA) analysis considering the compressive strength at the different concrete ages. It was observed that NPA, in the geopolymer concrete, improved the compressive strength compared to PCA. The NPA-based mixes achieved the highest 28-day compressive strength, 69 MPa, with about 27.8% more than the highest 28-day compressive strength achieved by the PCA-based mixes, 54 MPa. The obtained results revealed that the NPA has achieved the best improvement for both the workability, in terms of initial slump value and slump loss rate, and the compressive strength of GPC mixes compared to PCA.

The dynamics of marsh-channel slump blocks: an observational study using repeated drone imagery

Abstract. Slump blocks are widely distributed features along marsh shorelines that can disturb marsh edge habitats and affect marsh geomorphology and sediment dynamics. However, little is known about their spatial distribution patterns or their longevity and movement. We employed an unoccupied aerial vehicle (UAV) to track slump blocks in 11 monthly images (March 2020–March 2021) of Dean Creek, a tidal creek surrounded by salt marsh located on Sapelo Island (GA, USA). Slump blocks were observed along both convex and concave banks of the creek in all images, with sizes between 0.03 and 72.51 m2. Although the majority of blocks were categorized as persistent, there were also new blocks in each image. Most blocks were lost through submergence, and both decreased in area and moved towards the center of the channel over time. However, some blocks reconnected to the marsh platform, which has not been previously observed. These blocks were initially larger and located closer to the marsh edge than those that submerged, and they increased in area over time. Only 13 out of a cohort of 61 newly created blocks observed in May 2020 remained after 5 months, suggesting that most blocks persist for only a short time. When taken together, the total area of new slump blocks was 886 m2, and that of reconnected blocks was 652 m2. This resulted in a net expansion of the channel by 234 m2 over the study period, accounting for about 66 % of the overall increase in the channel area of Dean Creek, and this suggests that slump block processes play an important role in tidal creek channel widening. This study illustrates the power of repeated UAV surveys to monitor short-term geomorphological processes, such as slump block formation and loss, to provide new insights into marsh eco-geomorphological processes.

Properties of fibre-reinforced self-compacting concrete subjected to prolonged mixing: an experimental and fuzzy logic investigation

This article investigates the effect of prolonged mixing on the rheological properties and compressive strength of fibre-reinforced self-compacting concretes (FRSCCs). Twenty FRSCC mixes with five cementitious material contents (300, 350, 400, 450 and 500 kg/m3) and three types of fibres and dosages (polypropylene at 0.1%, steel at 1.0%, or synthetic at 1.0%) were first produced. The mixes were then subjected to four mixing intervals of 20 min each (total mixing time = 80 min). The rheological properties of the fresh FRSCC mixes were examined, and the corresponding compressive strength of the hardened FRSCCs was subsequently obtained. Overall, the results from slump flow, T50, V-funnel and L-box tests on fresh mixes, as well as the 28-day compressive strength on the hardened FRSCCs, were in line with previous results reported in the literature. The results show that all mixes lost their self-compacting properties after 80 min of mixing. It was also found that mixes with high cementitious material contents (500 kg/m3) and highest polypropylene fibre dosage were most affected by prolonged mixing, with average losses of 30% and 35% in rheological properties and compressive strength, respectively. Based on the test results, this study proposes a novel fuzzy logic approach to predict the slump loss and at 28-day compressive strength loss of FRSCCs subjected to prolonged mixing. This article contributes towards a better understanding of FRSCCs after prolonged mixing, which can help make informed decisions about their use in new and repaired concrete structures.

Pumping lightweight aggregate concrete into high-rise buildings

Lightweight aggregate concrete (LWAC), characterized with low density and high crushing strength to apparent density ratio, is a potential construction material for modern concrete structures. However, experiences in pumping LWAC to high-rise buildings are insufficient and the pumping pressure of fresh concrete may differ from normal weight concrete (NWC). Herein, three groups of shale lightweight aggregate (SLWA) were prepared to evaluate the workability of LWAC before and after pumping up to 102-m construction site. Water content and pressure loss are analyzed to understand the mechanism in slump variation of LWAC. A pumping pressure model is proposed based on friction assumption for horizontal and vertical pumping. The relationship between water content and ambient pressure is simulated. Pressure drop in pumping LWAC is found more than 4 times that in NWC at the same slump level. The main reason for large slump loss and pumping difficulty for LWAC lies in the water transportation process from mixture into porous aggregates.

Influence of nano zirconia on the mechanical and durability properties of high-performance concrete containing nano-silica

High Performance Concrete (HPC) was prepared by reinforcing with hybrid nanoparticles such as nano-SiO2 and nano-ZrO2 and the flowability, strength and durability of the concrete was investigated. Slump study showed that the prepared HPC displayed a slump loss with the addition of hybrid nanoparticles due to the absorption of water by hybrid nanoparticles. Experimental results showed that the inclusion of 10% nano-SiO2 and 5% nano-ZrO2 hybrid nanoparticles (mix code M5) enhanced the compressive strength of concrete and exhibited a maximum of 50.12 MPa and 76.4 MPa at 7 days and 28 days of curing due to the reduction of pore volume. Split tensile strength followed the same trend of variation as compressive strength and the mix code M5 showed the maximum split tensile strength of 5.33 MPa and 7.08 MPa cured at 7 days and 28 days respectively. Flexural study resulted that the mix code M5 exhibited a maximum flexural strength of 5.73 MPa and 7.38 MPa cured at 7 days and 28 days respectively owing to the restriction of crack ignition by reinforced hybrid nanoparticles. Rheological study reported that all the prepared concretes lost the weight by less than 1% and the chloride attack displayed maximum weight loss of 4% whereas alkaline attack showed less weight of concrete.

Effectiveness of the Use of Polymers in High-Performance Concrete Containing Silica Fume.

The incorporation of polycarboxylate ether superplasticizer (PCE)-type polymers and silica fume (SF) in high-performance concretes (HPC) leads to remarkable rheological and mechanical improvements. In the fresh state, PCEs are adsorbed on cement particles and dispersants, promoting the workability of the concrete. Silica fume enables very well-compacted concrete to be obtained, which is characterized by high mechanical parameters in its hardened state. Some PCEs are incompatible with silica fume, which can result in slump loss and poor rheological behavior. The main objective of this research is to study the influence of three types of PCEs, which all have different molecular architectures, on the rheological and mechanical behavior of high-performance concretes containing 10% SF as a partial replacement of cement. The results show that the carboxylic density of PCE has an influence on its compatibility with SF.

Study on Preparation and Mechanism of Concrete Slump Retaining Agent

Using acrylic acid and polyether polymer as the main raw materials, with hydroxyethyl acrylate monomer free radical copolymerization of polycarboxylic acid slump inhibitor, has the effect of reducing the slump loss of concrete. The slow release rate of concrete slump retaining agent synthesized with different ester ratios was studied, and the effects of different ester ratios, different ester ether ratios, and different ambient temperatures on the dispersion, dispersion retention, and hydrolysis rate of polycarboxylic acid slump retaining agent were systematically studied. The knowledge basis for the development of the slump-retaining agent with different sustained release effects. In engineering applications, the working performance of concrete can be controlled more effectively according to the length of the slow release time.

Effect of moisture content of recycled aggregates on workability, compressive strength and durability of concrete-A review

It is necessary to clarify the influence of different moisture contents of recycled aggregates (RA), including oven dry (OD), saturated surface dry (SSD), air dry (AD), etc., on the performance of recycled aggregate concrete (RAC) considering the time-dependent water absorption characteristic of RAs. By analyzing the previous literature, the effects of different moisture contents of RAs on the workability, compressive strength, and durability of RAC were discussed in detail. In addition, the microscopic mechanism was revealed based on the microstructure analysis. A lot of studies have shown that RAC prepared with RA in OD state had the largest fluidity when the same additional water was used. The slump loss of RAC decreases with the increase of water content of RAs, and when the moisture content of RA is higher than 50% of the water absorption of SSD, the slump loss is related to the additional method. The compressive strength and durability of RAC prepared with RAs in AD state were better than that prepared with RA in OD or SSD state. The shrinkage of RAC prepared with RA in OD state was greater than that prepared with RA in the SSD or AD state.

Application of nano scale stone powder and Grade III fly ash in high-performance concrete

Nanostone powder is an ultrafine powder with hydroxyl group on the surface after characteristic treatment. In the field of cement concrete, nanometer stone powder can increase the strength and durability of concrete due to its strong volcanic ash activity, microaggregate filling effect and crystal core effect. This paper prepared high-performance concrete with nano-grade stone ash and third-grade fly ash, mainly studying the effect of nano-grade fly ash on its performance (working performance, compressive strength, etc.). Silicate cement slurry is divided into fresh cement slurry and hardened cement slurry. At the same time, fine admixture particles can relieve the flocculation structure formed in the process of cement hydration, which can effectively reduce the loss of concrete slump. (The results showed that the working and mechanical performance of nano-grade stone powder or third-grade fly ash.

Experimental assessment of mechanical and physical performance of latex modified concrete with fine recycled aggregate

One of the most crucial building materials is concrete. However, producing concrete consumes a significant amount of natural resources. Attention has been focused on using concrete debris and recycling it in the building industry to solve this issue. This study investigates latex-modified concrete's physical and mechanical performance when replacing fine natural aggregates (FNA) with different percentages of fine recycled aggregates (FRA). The study includes conducting laboratory tests to investigate the workability, slump loss, compaction factor, compressive strength, ultrasound pulse velocity, absorption, and porosity. When replacing fine natural aggregates (FNA) with different percentages of fine recycled aggregates (FRA), it was found that there is an inverse relationship between the slump, compressive strength, compaction factor, and the percentage of RFA. The existence of SBR latex in concrete to form polymer modified concrete led to a higher decrease in workability compared to unmodified concrete. The absorbability increases as the proportion of fine natural aggregates are replaced by recycled fine aggregates, possibly due to the higher porosity of recycled fine aggregates. The same conclusion can be generalized to the results of the porosity test. However, adding the polymer improves the absorption resistance and reduces the porosity when replacing the fine natural aggregate with the fine recycled aggregate. Additionally, the outcomes demonstrated that SBR latex compensates for the compressive strength loss caused by recycled fine aggregates.

Workability and strengths of ternary cementitious concrete incorporating calcined clay and limestone powder

Problems associated with the production and utilization of Portland cement have necessitated the use of alternative or supplementary binders in concrete production. This study investigated the use of two supplementary binders; calcined clay (CC) and limestone powder (LP) as substitutes for cement in the production of concrete. Both the calcined clay and limestone powder were characterized using X-ray diffraction (XRD), X-ray Fluorescence (XRF) and Scanning Electron Microscope (SEM). Blended concrete mix proportions containing calcined clay and limestone powder were prepared and tested for fresh and hardened concrete properties including workability, compressive and splitting tensile strengths. The outcomes of this research showed that calcined clay is majorly amorphous with traces of crystal particles while limestone is all crystal particles. Based on oxides composition, calcined clay can be used as pozzolan while limestone powder can be best utilized as pore fillers. The addition of both calcined clay and limestone powder resulted in the loss of slump, although the effect is more pronounced in concrete blends containing calcined clay. While the inclusion of limestone powder caused a slight loss of strength in the blended concrete, it can still be utilized to achieve reasonably high strengths. Only concrete mix incorporating 10% of calcined clay gives a slight increase in strength, hence calcined clay can be utilized to a limited volume in concrete production.

EFFECT OF CAST-IN-PLACE CONCRETE STRENGTH EVOLUTION ON PRESSURE TUNNEL LININGS FOR THE HYDROPOWER PLANT

This study aims to explore how cast-in-place concrete strength evolution influences pressure tunnel linings for the hydropower plants. Although conventional concrete has been so far implemented broadly for constructing many engineering structures in general and pressure tunnels in particular, its quality and performance can still be improved using diffirent chemical admixtures. Advanced concrete with the usage of water-reducing admixture has been studied in this paper. Indeed, the mix that involved the admixture with 0.6 and 0.9% of cement content has outperformed one without the admixture usage. Regarding the fresh state, in comparison with the conventional concrete, the advanced concrete did not present the slump loss even though the time retardation was 90 minutes. Besides, the one with 0.9% admixture was still pumpable with a time retardation of two and a half hours. At the hardened state, the advanced concrete excelled in the designed strength class by almost 20%, particularly it had a high early-age strength that provides construction accelerating. The advanced concrete with 0.9% admixture usage has been used successfully for the pressure tunnel linings of the Song Bac hydropower plant, thank to a high early-age strength, it was acceptable for an early removal of slide formwork after 3 days. Because of that, the time to complete one kilometer tunnel of this project was merely half of the counterpartner Tan Giang hydropower plant that involved conventional concrete. Despite the 10% increment of expenditure for the admixture usage in the advanced concrete, the total investment cost has been reduced by 16%. Keywords: Water-Reducing Admixture, Accelerator, High Early-Age Strength, Slide Formwork, Concrete Linings DOI： https://doi.org/10.35741/issn.0258-2724.58.1.53

Study on the multiscale properties of cement-based materials containing nano-bubble water

In this work, the effects of nanobubble water (NBW) on the durability, rheology, macromechanics, and microscopic properties of cement-based materials were investigated. NBW did not significantly improve the fluidity and compressive strength of the concrete with strength grades below C25; however, it did significantly improve the fluidity and inhibit the slump loss of concrete with strength grades above C30, while the compressive strengths of the samples at different ages increased to varying degrees. NBW could also improve the durability of the concrete (sulfate resistance, carbonation resistance, and single-side freeze-thaw resistance) to varying degrees. The hydration temperature test, XRD, TGA/DTG, and MIP results indicated that NBW promoted the hydration reaction process and the generation of hydration products such as CSH colloids and CH crystals, which could effectively improve the internal structure of the cement paste, thereby further affecting the macroscopic properties. The mechanism of NBW was such that the high potential adsorption force on the surface of the fine bubbles increased the number of ion nucleation sites in the suspension, which was beneficial for increasing the effective hydration products of the cement in the early stage.

Valorization of macro fibers recycled from decommissioned turbine blades as discrete reinforcement in concrete

The extensive use of glass fiber-reinforced polymer (GFRP) composites has inevitably resulted in a large amount of FRP waste, posing a significant environmental threat. A recent study performed by the authors’ group of the present study pioneered a new mechanical method of recycling GFRP wind turbine blades into macro fibers, in which the macro fibers characterized by a fixed-length have been produced using a manual process of low efficiency and high cost, making it impossible for use in a practical application. In the present study, a shredding machine has been therefore used to efficiently process waste GFRP wind turbine blades into macro fibers of hybrid lengths lesser than 100 mm for being incorporated into concrete. A series of tests were carried out to investigate the properties of the resulting concrete, and the test results of beam specimens were then analyzed using a twice inverse analysis approach. The results of compression tests and four-point bending tests showed that the incorporation of recycled macro fibers led to a slump loss of 54%, a compressive strength reduction of 14.07%, a flexural strength improvement of 37.85% and a significant flexural toughness enhancement of 36.8 times at a fiber volume ratio of 2.5%, as compared to those of plain concrete. The direct-tensile strength and the corresponding tensile strain obtained by a twice inverse analysis approach were about 2.26 MPa and 134 με, respectively, as predicted by the inverse analysis based on flexural load-deflection curves. The macro fibers processed using a shredding machine are feasible for enhancing the performance of the resulting concrete, and can be economic-efficiently used for industrial scale applications.

Understanding the workability of alkali-activated phosphorus slag pastes: Effects of alkali dose and silicate modulus on early-age hydration reactions

Understanding the workability of alkali-activated phosphorus slag (AAPS) pastes is fundamental for their efficient application. This study revealed the novel mutual inhibition mechanism through which the alkali dose and silicate modulus affect the workability of AAPS pastes based on the hydration reaction. The slump loss of NaOH-activated phosphorus slag (NAPS) paste was slow, and that of waterglass-activated phosphorus slag (WAPS) paste was faster because the soluble Si in waterglass accelerated the dissolution of the phosphorus slag (PS). At a moderate waterglass modulus, the slump losses of the WAPS pastes were slow because the moderate [Al]/{[Ca]+[Mg]} ratio in the pore solution minimized the difference in the magnitude of mutual inhibition between Ca, Mg and Al, causing all hydrates to form slowly. However, at higher and lower waterglass moduli, the WAPS pastes exhibited fast slump losses because hydrates with excess elements formed rapidly due to the excessively high or low [Al]/{[Ca]+[Mg]} ratio.

Study on axial compressive behavior and damage constitutive model of manufactured sand concrete based on fluidity optimization

Due to the adsorption effect of manufactured sand on water reducer, the method of adding water reducer is often used to improve the fluidity of concrete mixture, which may change the strength of manufactured sand concrete. This paper systematically studies the manufactured sand concrete with different strength grades of C30, C40, C50, C60, C70, C80 prepared with basic water reducer dosage (1 time) and optimized water reducer dosage (1.65 times), and designs slump, slump loss, uniaxial compression and pore content tests for manufactured sand concretes with the same strength grade. The results show that optimized dosage of water reducer can significantly increase the fluidity, peak stress and elastic modulus of manufactured sand concretes with the same strength grade and reduce their slump loss, peak strain and pore content. Combined with Lemaitre damage mechanism, the total damage of manufactured sand concrete is divided into initial damage and load damage. The initial damage is caused by different fluidity of manufactured sand concrete. The greater the fluidity, the less initial damage will be. The influence of initial damage on the concrete stress-strain relationship is analyzed. As the initial damage increases, the total damage will increase, the strength and elastic modulus of the concrete will decrease. This is due to the fluidity changes the pore structure inside the concrete.