Fine Concrete Research Articles

Interactions of Cd2+, Co2+ and MoO42− Ions with Crushed Concrete Fines

Construction and demolition activities generate approximately two thirds of the world’s waste, with concrete-based demolition material accounting for the largest proportion. Primary aggregates are recovered and reused, although the cement-rich fine fraction is underutilised. In this study, single metal batch sorption experiments confirmed that crushed concrete fines (CCF) are an effective sorbent for the maximum exclusion of 45.2 mg g−1 Cd2+, 38.4 mg g−1 Co2+ and 56.0 mg g−1 MoO42− ions from aqueous media. The principal mechanisms of sorption were determined, by scanning electron microscopy of the metal-laden CCF, to be co-precipitation with Ca2+ ions released from the cement to form solubility limiting phases. The removal of Co2+ and MoO42− ions followed a zero-order reaction and that of Cd2+ was best described by a pseudo-second-order model. The Langmuir model provided the most appropriate description of the steady state immobilisation of Cd2+ and Co2+, whereas the removal of MoO42− conformed to the Freundlich isotherm. Long equilibration times (>120 h), loose floc formation and high pH are likely to limit the use of CCF in many conventional wastewater treatment applications; although, these properties could be usefully exploited in reactive barriers for the management of contaminated soils, sediments and groundwater.

Preparation and properties of recycled fine powder foam concrete

With the rapid development of the construction industry brought by the accelerated process of urbanization, the problem of random stacking and landfill of waste concrete can be seen everywhere, which seriously affects the environmental health. The secondary utilization of waste concrete as recycled aggregate has become a research hotspot. This paper mainly studies the influence of the cementing material system of recycled fine powder foam concrete on the water absorption performance of recycled fine powder foam concrete, and explores the feasibility of using recycled fine powder to prepare foam concrete. The experiment also used recycled fine powder instead of some cement to prepare foam concrete. The effects of the amount of recycled fine powder, the amount of hydrogen peroxide and the ratio of water to binder on the compressive strength, water absorption, thermal conductivity and microstructure of the foam concrete were studied. The results showed that the water absorption rate of recycled fine powder foam concrete increased with the increase of red brick powder content, but the water absorption rate gradually increased. When the content of hydrogen peroxide is 6%, the ratio of water to binder has a greater influence on the thermal conductivity of foam concrete. When the amount of hydrogen peroxide is higher, the influence of water binder ratio on thermal conductivity decreases.

Laboratory-scale study and semi-industrial validation of viability of inorganic CDW fine fractions as SCMs in blended cements

The construction industry and more particularly cement manufacture industry are European Green Deal strategic priorities for the circularity of Europe’s construction and demolition waste (CDW) stream with a view to reducing CO2 emissions. The industry is engaged in a number of strategies to that end, one of which is to manufacture new low-carbon, lower clinker/cement ratio cements by replacing portland clinker with inorganic fractions of CDW featuring hydraulic or pozzolanic properties. Against the backdrop of that global challenge, the present study explores the cementitious potential of the limestone and siliceous concrete fines and shatterproof building glass found in CDW as supplementary cementitious materials (SCMs) in new blended cements. The research was conducted in two stages: generation of new laboratory-scale knowledge; and industrial validation of the viability of using the highest volume waste streams. The laboratory-scale findings revealed that the presence of the filler effect and pozzolanicity in micronised inorganic fractions of concrete and building glass waste induces the neoformation of hydrated phases and C-S-H gel. Those two developments improve the short- and long-term physical and mechanical properties of the new blended cements at optimal replacement ratios of 5–7%. The order of material effectiveness in shortening setting times, increasing the heat of hydration and maintaining mechanical strength was observed to be as follows: limestone concrete > siliceous concrete > glass waste. Laboratory analysis was followed by a pilot study consisting in the manufacture of 184 t of blended cement in which 5% of the clinker was replaced by recycled concrete. Higher product performance than the commercial reference cement confirmed the industrial, technical, economic and environmental viability of the new product, estimated to hold potential for CO2 emissions abatement on the order of 41 kg CO2 eq./t of cement, which could translate into 80 Mt CO2 eq./year worldwide.

Study on Flexural Properties of Basalt Fiber Textile Reinforced Concrete (BTRC) Sheets Including Short AR-Glass Fibers

Experimental investigations were carried out to determine the mechanical properties of fine concrete with short AR-glass fibers including the effects of fiber content and length. Also, the basalt fiber textile reinforced concrete (BTRC) sheets with short AR-glass fibers were tested under four-point bending, and the effects of the number of fiber textile layer and fiber length on the flexure properties were emphatically analyzed. The results show that the mechanical properties of fine concrete with fibers were mainly related to fiber length and content, the mechanical properties of fibers reinforced fine concrete increase with the increase of fiber length, and the comprehensive mechanical properties of fine concrete materials are the best when the AR-glass fiber content is about 5%. The flexure performance tests of BTRC sheets show that the strength and the deformation capacity of sheets increase with the increase of the number of fiber textile layers. The short AR-glass fibers can also effectively improve the strength and deformation capacity of BTRC sheets, and the cracking load and ultimate displacement can be respectively increased by up to 106% and 268% compared with BTRC sheets without short fibers. For the multi-fiber compound reinforced concrete sheets, the fiber textile can provide tension in the desired direction, and the short AR-glass fibers can improve the cracking resistance and toughness of sheets.

Surface characterization of carbonated recycled concrete fines and its effect on the rheology, hydration and strength development of cement paste

Carbonation treatment can effectively improve the performance of recycled concrete aggregate and fines due to the reactions of CO2 with CH and C–S–H gel of cement paste. To better understand the mechanisms involved in the performance improvement, the surface properties of carbonated recycled cement paste powder (CRP) and its effect on the rheology, hydration and strength development of cement paste was studied. The results showed that during the carbonation, the surface of CRP was covered by a layer of amorphous silica gel. The generated CaCO3 was wrapt by the silica gel and seldom exposed. The silica layer led to the poor flowability of CRP-cement paste due to that the silica gel on the surface of CRP has a strong affinity for H2O. During the very early hydration, the silica gel dissolved and then CaCO3 was exposed. CaCO3 is capable of chemically absorbing Ca2+, which facilitated the nucleation of C–S–H nuclei and stabilized the C–S–H phase. As a result, the C–S–H grew densely, uniformly and perpendicularly on the surface of CRP. In addition, the chemically absorbing Ca2+ enabled the chemical bond to be formed between CaCO3 and C–S–H. Due to increased C–S–H resulted from reactions of silica gel with CH at the interface and the stronger bond formed between CaCO3 and C–S–H, the interface between CRP and hydration products was much stronger than that between recycled cement paste powder (RP) and hydration products.

CO2 Utilization via Direct Aqueous Carbonation of Synthesized Concrete Fines under Atmospheric Pressure.

Mineral carbonation using alkaline wastes is an attractive approach to CO2 utilization. Owing to the difference between waste CO2 and feedstock CO2, developing CO2 utilization technologies without CO2 purification and pressurization is a promising concept. This study investigated a potential method for CO2 utilization via direct aqueous carbonation of synthesized concrete fines under atmospheric pressure and low CO2 concentration. The carbonation reaction with different solid–liquid ratios and different concentrations of introduced CO2 was examined in detail. Under basic conditions, a CO2 uptake of 0.19 g-CO2/g-concrete fines demonstrated that direct aqueous carbonation of concrete fines under atmospheric pressure and low CO2 concentration is effective. The CaCO3 concentration, degree of carbonation, and reaction mechanism were clarified. Furthermore, characterization of the carbonated products was used to evaluate ways of utilizing the carbonated products.

Utilization of recycled concrete fines and powders to produce alkali-activated slag concrete blocks

This paper investigated the properties of alkali-activated slag (AAS) concrete blocks incorporated with recycled concrete fines (RCFs) and recycled concrete powders (RCPs). They were used as the fine aggregates and the binder in AAS concrete blocks, respectively. The influence of RCFs and RCPs content on water absorption, apparent porosity and compressive strength of AAS concrete blocks was examined. The reactivity of RCPs, mineral changes and microstructure of AAS concrete blocks were characterized by the isothermal calorimetry and X-ray diffraction and scanning election microscope, respectively. The test results indicate that incorporating RCFs and RCPs can decrease water absorption and apparent density of AAS concrete blocks, but an excessive amount of RCFs and RCPs has an opposite impact on these properties. Compressive strength of AAS concrete blocks is enhanced by about 47% when 75% sand is replaced by RCFs. This is mainly attributed to the reaction of un-hydrated cement in RCFs and the internal curing through the RCFs. RCPs have been proven to have a certain degree of reactivity in the alkaline activation. As a result, replacing 20% slag by RCPs can also improve the compressive strength of AAS concrete blocks by about 13%. The AAS concrete blocks produced with RCFs and RCPs possess a satisfactory physical and mechanical properties required for non-load bearing concrete blocks. It is feasible to utilize RCFs and RCPs as the partial replacements of the sand and the binder in AAS concrete blocks, respectively.

РАЗРАБОТКА СОСТАВОВ САМОУПЛОТНЯЮЩЕГОСЯ БЕТОНА НА ОСНОВЕ БЕТОННОГО ЛОМА С ИСПОЛЬЗОВАНИЕМ СТРУКТУРНЫХ ХАРАКТЕРИСТИК

Abstract. Huge amount of recycled concrete is formed when dismantling of buildings. The paper describes an efficient application of recycled concrete aggregates and concrete grinding fines to obtain technological, economic and ecological benefits. The possibility of effective application as materials for self-compacting concrete with the use of crushed concrete and recycled concrete fines is shown. The use of filler in self-compacting concrete mixtures obtained by activation of concrete grinding fines with polycarboxylate-based superplasticizer is shown. This paper presents the results of research of self-compacting concrete produced with recycled concrete aggregates and activated filler. The physical and mechanical characteristics of coarse aggregate, grain distribution of aggregates and sand proportion in aggregate mix, design of self-compacting concrete mixture and its structure properties with use mathematical experiment planning method were carried out. This method applies in the design of the self-compacting concrete mixture by solving the system of equations. The equations obtained by corresponding mathematical models. The obtained mathematical models include argumentative characteristics defined by the end of structure formation. The optimal content of filler in self-compacting concrete mixture is determined. The optimal grinding mode of the equipment with specified specific surface area of the filler is obtained. The grain-size composition of mixture consisting of quartz sand and crushed concrete aggregate with fraction of 5-10 mm based on term of maximum approximation to the Fuller ideal gradation curve is designed.

Mitigating inclusion-induced shrinkage cracking in cementitious composites by incorporating recycled concrete fines

Recent studies on utilization of recycled concrete have demonstrated that usually discarded finest fractions can be incorporated into cementitious composites without scarifying their structural performance. It has been shown that these fines can increase the resistance of a cementitious matrix to tensile stresses and reduce shrinkage, and that these effects can be boosted by addition of mineral admixtures. Such findings led us to a consideration that incorporating recycled concrete fines into a concrete mix could possibly mitigate aggregate-induced shrinkage cracking. Here, this hypothesis was put under scrutiny in a comprehensive experimental-numerical study, confirming that blending Portland cement with recycled concrete fines can mitigate inclusion-induced shrinkage cracking, especially when combined with fly ash. The results of coupled hygro-mechanical modeling indicate that incorporating recycled concrete fines leads not only to a decrease of shrinkage but also increases fracture energy and thus has a major impact on the reduction of micro-cracks between inclusions.

Kinetics of enforced carbonation of cement paste

The carbonation mechanisms of ground, hydrated cement pastes that mimic recycled concrete fines are investigated under direct wet carbonation. The carbonation is a sequential processes including dissolution of the hydrates, transport of the dissolved material to the precipitation sites and precipitation of the reaction products. During the first stages of carbonation, when portlandite reacts, the reaction is limited by the amount of dissolved CO2 and potentially by the calcite precipitation rate. When portlandite is depleted, the kinetics is dominated by the dissolution of other hydrates and diffusion of calcium into the solution. The main carbonation products are calcite and an alumina-silica (hydrate) gel. The hydrotalcite-like phase appears to be stable towards carbonation under the experimental conditions employed in this work. The CO2 concentration and the paste composition have a limited influence on the reaction mechanisms as well as on products formed.

Small‐scale plate tests with fine concrete in experiment and first simplified simulation

AbstractIn the following article impact experiments from experimental and numerical point of view will be described. In order to keep the number of parameters to be varied manageable, the focus was firstly on similar plain concrete plates. The experiments were carried out with the aim to collect reference values and to simulate these experiments as basis for further investigations. The only parameter that has been changed was the impact velocity. The experimental part of the publication deals with manufacturing of the specimens, the experimental setup, the execution of the experiments, the measured values, and a brief evaluation of the results. The numerical part of the publication deals with the computation of experimental results using the simulation program LS‐Dyna. In this context, it will be explained how the model was created and which boundary conditions and material models were used. Furthermore, the calibration of the materiel law is described. Subsequently, a comparison between the experimental and simulated results is carried out. The focus of the further investigations will be the consideration of concrete layers reinforced with textiles under impact load. The work presented here deals with the matrix material of the textile reinforced concrete and thus laid the foundation for these investigations.

Producing a sustainable type of concrete enhanced by industrial polystyrene

This research includes studying the possibility of producing a new type of no fine concrete by replacing granules of coarse aggregates with grains resulted from the fragmentation of industrial waste of polystyrene. This replacing is with different volumetric proportions of coarse aggregate, and theses volumetric ratios were equal to (5%, 10%, 15% and 25%). Waste plastic fibers (WPFs) resulting from cutting of soft drinks bottles were added for strengthening this new kind of concrete. Mixing ratio was equal to (1:5) (cement: coarse aggregate) by weight. One reference mix was produced for comparative purpose. Compressive strength, flexural strength and density tests were conducted.Compressive strength values of the new sustainable concrete were ranged from 10 MPa to 12.4 MPa at age of test equal to 28 days, while the lowest value of the density of this concrete at the same age reaches 1937 kg/m3, and highest value of modulus of rupture was equal to 2.36 MPa at 28-day age test.

Fines isolated from waste concrete as a new material for the treatment of phosphorus wastewater.

Waste concrete is a key component of construction and demolition (C&D) waste produced in billions of tons. Exploring new technology for recycling waste concrete has become a global concern. Meanwhile, phosphorus (P) removal from wastewater consumes lots of natural minerals, leading to a heavy burden on the environment. In this study, the cement paste powder (HCPP) was used to remove phosphorus from wastewater. The results indicate that both HCPP and thermally modified HCPP (MHCPP) are effective phosphorus removal materials, with a maximum P-binding capacity of 3.9-mg P/g HCPP and 31.2-mg P/g MHCPP, respectively. The phosphorus removal mechanism of HCPP and MHCPP was also proposed: (1) Ca2+ and OH- can release from the surface of the HCPP or MHCPP to wastewater, forming a high-alkaline and Ca-rich solution; (2) hydrolysis of phosphorus species in the high-alkaline solution environment creates HPO42- species; (3) the HPO42- combines with Ca2+ and H2O, resulting in the formation of brushite; (4) the brushite precipitated from wastewater and adhered on the surface of the HCPP or the MHCPP particles. The study provides a new and low-cost material for treatment of phosphorus wastewater. Further, the study also offers a new approach for reusing of waste concrete fines.

Study of the Suspension Stability of Titanium Dioxide of Anatase Modification for Self-Purifying Fine Concrete

The suspension stability of the titanium dioxide of anatase modification, obtained by ultrasonic dispersion (USD) at the ultrasound frequency of 35 kHz in the aqueous medium of the stabilizer for self-purifying fine concrete as a finishing material for building envelope, is studied. The extreme dependence of the zeta potential on the ultrasonic dispersion parameters of titanium dioxide in the aqueous medium of the surfactant on the basis of sodium salts of naphthalene sulfonic acid and formaldehyde condensation products is established. Various variants of the sequence of the surfactant introduction into the titanium dioxide suspension are analysed. The ratio between TiO2 and the stabilizer, at which the zeta potential exceeds the threshold value of 30 mV and the suspension stability is maintained during 15 days, is determined. The optimal sequence of the suspension components introduction and the ultrasonic dispersion time are established. The influence mechanism of intermittent surfactant introduction on stabilization of the suspension of titanium dioxide of anatase modification is offered. The dependences of the fine concrete strength on zeta potential of the studied suspensions are obtained.

Reuse of fines from ready-mix concrete washing slurries

Concrete waste slurries coming from the washing of concrete mixer trucks in the manufacture of ready-mix concrete generate high costs and environmental impacts. In this work, we examined the consumption of raw materials, water, and generation of wastes for three Brazilian ready-mix concrete plants (that used different waste management strategies). The reuse of concrete slurry fines was also investigated in new concretes considering the waste management scenarios, production and operational costs. The strategy to recover fresh concrete provided the best scenario since it reduced significantly operational costs, despite the inclusion of new production cost, i.e. the hydration stabilizer additive. The replacement of sand with 1 vol.% concrete slurry provided adequate rheological conditions for concretes, when the water content increased up to 6 wt.% or added 0.3 % m.c. of polycarboxylate-based additive. The marginal increase in the production cost can also be compensated by the reduction of the disposal operational costs. The reuse strategy was not enough for the total elimination of concrete fines, requiring market diversification (e.g. pre-cast concrete products); but fines availability can be very limited.

Recovery of residual anhydrous clinker in finely ground recycled concrete

The costs of construction waste handling, a scarcity of landfill sites, and requirements for sustainable construction have placed recycling of concrete—the most abundant construction material in the world—under scrutiny. Unlike recycling of aggregates, utilization of sub-sieve fractions from recycled concrete has not yet been adopted in the construction industry. In this study, we investigate the possibility of recovering residual anhydrous clinker embedded in grains of stripped mortar within these fines. Different samples of waste concrete were finely ground and studied using microscopy and chemical analyses to assess the amount of residual clinker. Its contribution to hydration processes was measured by calorimetry, and the impact of recycled concrete fines on mechanical properties of cement pastes was tested. The results indicate that residual anhydrous clinker is present in waste concrete and can be recovered by grinding. Replacing Portland cement with the recycled material in pastes led to a significant increase of tensile strength, while deterioration of compressive strength was negligible when the concrete fines contained higher amounts of residual clinker and when the amount of fines did not exceed 30% of Portland cement weight.

An experimental investigation on light-weight concrete blocks using vermiculite

Abstract Lightweight concrete block finds a wide range of application within the construction industry. Concrete block having a dry density of approximately 300 kg/m3 to a most of 2000 kg/m3 are deliberate to be light-weight concrete. By using the lightweight concrete can reduce the self-weight of the structure. Thereby it reduces the price of construction. During this study No fine concrete is employed it's a combination of cement, water, and coarse aggregate with fines (sand) omitted. The concrete mix has cement, coarse aggregate and vermiculite. Fine aggregate is completely neglected. Three trail mix is followed as 1:1:2, 1:1.5:1.5 and 1:2:1. The cubes are casted and tested within the compression testing machine. The take a look at results are compared with IS 2185-1 (2005) observe whether those concrete blocks will be utilized in the construction method.

Optimization of Formula and Technological Parameters of Fiber-Reinforced Concrete Manufacturing

The development of modern construction technologies requires the development of efficient building materials with a unique property set and the improvement of existing ones. Fiber-reinforced concrete is one of the types of effective composites that meets the specified requirements, ensuring the structures operation reliability. The difficulty of achieving its maximum physical and mechanical characteristics is due to the complexity of the fiber equal distribution in the concrete matrix. Studies aimed at the optimization of the formulation and technological manufacture parameters of fiber-reinforced fine concrete, have revealed that from the perspective of obtaining products with optimal physical and mechanical characteristics, it is most feasible to introduce the agglutinant sand (cement + sand) of pre-prepared suspension from fibers, water of mixing and naphthalene formaldehyde plasticizer. Optimal dosages of input products were also revealed (basalt fiber, cement, plasticizer), which made it possible to create mixes of fine concrete and products based on it with class B25-B60 for compressive strength and Btb2,8-Btb6,0 for bending, frost resistance not less than F300.

Effect of Dosage of Redispersible Powders on the Properties of Fine Concrete

The RPP introduction has been established up to 3% by weight of the dry concrete mix is ​​accompanied by a decrease in the fine-grained concrete tensile strength in compression to 40% and in tension during bending to 15%. The relationship between the tensile strength limit in bending and compression for the studied materials is invariant to the cement and RPP type. With the concrete tensile strength in tensile bending increase, there is a weak tendency to a decrease in the adhesion ratio value to the concrete base and tensile strength. The adhesion amount to the concrete base with RPP increasing dosage can either increase or decrease after a certain limit, depending on the cement properties. The maximum increase in adhesion to the concrete base was 37%, while the decrease in the concrete elasticity initial modulus was 26%.

Application of expanding cements for sprayed concrete in tunnel construction

Introduction. The paper substantiates the actuality of the problem connected with obtaining efficient fine concretes possessing enhanced crack resistance, tightness, and duration for tunnel construction. This aim is pursued with the application of expansive cements (EC).
 Materials and methods. Various types of expansive agents were used in composition binders. Portland cement PTs 500 D0 was taken as the basic Portland cement. Studying hydration and structure formation processes during hardening of the ECs and EC-based concretes was executed utilizing a system of physicochemical methods. Assessment of construction and technical properties of the fine concretes based on composition binders was accomplished using standard research methods.
 Results. Analysis results are given for the effect of type and amount of the expansive agents on strength and volume deformation values of the concretes used in tunnel installation construction. Improvement of physical, mechanical, and technological properties and performance of sprayed concrete is shown. A general mechanism of influence of expansive additives (EA) on fine concrete properties is established. A classification of expansive cements for solving various tasks in tunnel installation construction is suggested.
 Conclusions. EA application efficiency is theoretically substantiated and experimentally proved for the case when the EA is used as an active agent in the composition binder for sprayed concrete in tunnel construction. General enhancement of technical indicators of concrete mixture and concretes is determined. EA classification is suggested for the different extent of hydrated EA expansion and various construction tasks. Replacement of standard Portland cement for an EC for underground structures concrete used in tunnel construction provides a significant increase in their maintainability.