High Early Strength Research Articles

Experimental Research on Compressive and Shrinkage Properties of ECC Containing Ceramic Wastes Under Different Curing Conditions

Engineered cementitious composites (ECCs) suffer from high shrinkage and low early strength due to large dosage of cementitious materials and slow hydration of fly ash. This study aims to improve compressive properties and reduce drying shrinkage of ECC using ceramic wastes and hydrothermal curing. Experimental results have indicated that ceramic polishing powder (CPP) and recycled ceramic sand (RCS) exert opposite effect on the compressive strength of ECC. Hydrothermal-cured ECC enhances elasticity modulus and compressive strength and reduces later drying shrinkage as compared with that under standard curing. A CPP dosage of 35% and a hydrothermal curing regime with a temperature of 70°C and age of 7 days are recommended for the engineering application of ECC.

Long-term durability properties of geopolymer concrete: An in-depth review

Geopolymer concretes (geocretes) are considered as eco-friendly materials for various building applications. Geocrete has high early strength, less consumption of natural resources, cost-effectiveness, capacity to form different structural configurations and to remain intact for extended periods without repair works. Meanwhile, geocretes have still exhibited an unstable behavior over time compared to traditional cementitious composites. To overcome this disadvantage, hundreds of studies have focused on the improvement of the microstructure of geocretes with a wide range of improved durability characteristics. Therefore, the review paper has an objective to make available an inclusive review on the production of supplemental-cementing-materials (SCMs), their economic returns, environmental and durability impacts, the conceptual model for geopolymerization, durability affecting factors, and function and long-term durability properties of geocrete. It is concluded that geocrete demonstrated a better resistance against aggressive environment compared to normal concrete, due to its less porous structures. Moreover, it is found that the strength of alkali-activated concrete was found to improve in chloride environment, unlike OPC based concrete. It is also concluded that, the presence of GGBS and MK in alkali-activated materials reduces its alkali-silica reactivity while it is recommended to use high calcium FA in geocrete production for durable concrete and geopolymerization. The higher the molarity of NaOH solution for a given quantity of Na2SiO3 the faster the geopolymerization process and the higher the compressive strength of concrete corrosion current than the OPC concrete. Further long-term durability studies are required to provide test methods and validation techniques since most studies focus on the 28-day curing regime.

Experimental investigation on mechanical strength and microstructure of cement paste by electric curing with different voltage and frequency

To understand the effects of direct electric curing condition on the mechanical strength and microstructure of cement paste, a series of experiments were carried out to investigate the effects of alternative current voltages and frequency on compressive strength of samples. And the corresponding microstructure of samples were also analyzed by several measurements including X-ray diffraction, thermogravimetric analysis, scanning electron microscopy and mercury intrusion porometer. The results show that alternative current electric voltage and frequency can greatly influence the early compressive strength of a cement paste. And a suitable electric curing condition can make hardened cement paste keep a steady growth of compressive strength and excellent microstructure. The Joule heat of direct electric curing on cement paste is the main reason that accelerates the hydration and improve the early strength development of sample. This study will provide an important technical support for exploring low carbon rapid electric curing method to produce green high early strength cement concrete prefabricated element.

Effect of Different Cracking Mitigation Measures on High Early–Strength Concrete Performance

AbstractEarly-age cracking may occur in high early–strength (HES) concrete repair slabs used for full-depth repairs in jointed plain concrete pavements (JPCPs) due to the early-age volume changes. ...

Mechanical Strength of Graphene Reinforced Geopolymer Nanocomposites: A Review

The emergence of high-strength graphene marks a new milestone in the material science field. With only a small percentage inclusion into the matrix system, this organic nanoparticle could tremendously improve the strength in vast arrays of composites. At the same time, there is a growing interest in using the low-cost, lightweight, and high early strength geopolymer as the new binder for concrete. Compared to the traditional Ordinary Portland Cement (OPC), geopolymer emits 80% less CO2 during its production while exerting similar strength. Thus, the geopolymer has the potential to commercialize as new and green concrete. Geopolymer is a mixture of aluminosilicate powders and alkaline solutions. When incorporated with nano-sized graphene, the material forms a composite known as Graphene Reinforced Geopolymer Nanocomposite (GRGN). The addition of graphene enhances the strength of geopolymer, which can further improve its competitiveness. However, this depends on several factors, including the types of graphene, the surface modification of graphene, and the concentration of alkaline solutions. Generally, the presence of graphene alters the porous structure of geopolymer into a substantially filled porous structure, thus increasing compressive strength and flexural strength. On the other hand, Graphene Oxide (GO) undergoes a chemical reduction in the alkaline solution, producing epoxy functional groups. The chemical treatment results in two conditions which are weak interaction between graphene and geopolymer matrix, and better graphene dispersibility in geopolymer matrix. This review also highlights the analytical modelling aspect of GRGN. The dissolution of Si(OH)4 and Al(OH)4- from the aluminosilicate source was consistent with experimental work and analytical modeling, while the dissolution of Si–OH on the surface-modified graphene indicated otherwise. Therefore, this paper will provide an insightful review of the GRGN mechanical properties.

Laboratory Study of Deformation Behaviour of Two New Reinforcing Polymeric TSLs and Their Potential Application in Deep Underground Coal Mine.

Thin spray-on liner (TSL) is a surface protection technology used by spraying a polymer film, which is widely used for mine airtightness and waterproofing. A reinforcing TSL can replace steel mesh, which is a new method for roadway support. This paper reviews the development of a reinforcing TSL. Considering the deterioration of geological conditions in deep underground mining and the demand for reinforcing automation, two kinds of polymeric reinforcing TSL (RPTSL) materials are developed. The mechanical characteristics of the new TSL materials are studied experimentally. Results show that the average compressive strength, tensile strength, cohesion, and internal friction angle of the two TSL materials are 52 and 32 MPa, 12 and 8 MPa, 6.2 and 17.2 MPa, and 33.6° and 25.9°, respectively. The bonding strength between the two materials and coal is greater than the tensile strength of coal itself, and the mechanical properties of the material for comparison are lower than those of both materials. Based on the TSL support mechanism, we examine the application of the two TSL materials to the mining environment and compare the mechanical properties of polymer materials and cement-based materials. The advantages of polymer materials include versatile mechanical properties, good adhesion, and high early strength. This study provides a new support material to replace steel mesh for roadway surface support, which satisfies the needs of different surface support designs under complex geological conditions, and promotes the automation of roadway support.

High-early strength concretes modified with polycarboxylate admixture on different cement types

Early and grade strength of modified concrete on different cement types (CEM II/A-S 42,5 and pozzolanic cement CEM IV/A(P) 42,5 R-SR) for concrete pavements repair was explored. Application range of the polycarboxylate modifier was 0.8-1.4% by weight of cement. All concrete compositions had equal workability (slump 5…9 cm). The aim of the investigation was to determine the optimal volume of the polycarboxylate modifier to achieve high strength indicators for repair material at the early and grade age.High-strength concrete of grades C 50/60 and C 40/50 were obtained, with early strength at the 3 days age above 35 MPa, which allows them to be used as a repair concrete material for rigid road pavements.X-ray phase analysis confirmed the positive effect of the polycarboxylate admixture in the structure formation of concrete. With an increase in the dosage of the BASF MasterGlenium SKY 608 admixture to 1.2…1.4%, the intensity of the diffractogram lines, which corresponds to the metastable hydration phase in the cement-sand matrix, decreased for concretes on both cement types.

Rheology of Cement Pastes with Siliceous Fly Ash and the CSH Nano-Admixture.

The use of fly ash in cement composites adversely affects its mechanical properties during the first days of mixture curing. Modern technology, in the form of an admixture containing the hydrated calcium silicates, allows to accelerate the hardening and binding process of concrete. In this paper, studies on the influence of the admixture on properties of concretes with the ordinary Portland cements (OPC) containing the addition of siliceous fly ash (FA) have been carried out. As part of the experimental research, the authors conducted a series of studies for cement pastes modified with the addition of FA and the CSH nano-admixture (NA). In order to compare the mixtures, the following tests of cement pastes were carried out: the compressive and flexural strength, heat of hydration, SEM and rheological shrinkage. The mechanical parameters were tested after 4, 8, 12 and 24 h. The hydration heat test and microstructure analysis were carried out during the first 24 h of the concrete curing. All tests were carried out on the standard samples. On the basis of the heat of hydration test, much higher hydration heat was found in mixtures modified with the NA. During the shrinkage test, a positive effect of the NA was observed—the shrinkage during the first 28 days of mixture curing was lower than in the reference samples. The application of the CSH nano-admixture to cement pastes with the addition of FA has brought positive effects. Apart from a significant increase in strength in the first 24 h of mixture curing, a reduction in the rheological shrinkage was observed. The admixture can be successfully used in the ash concretes, in which a higher early strength is required.

Application of Advanced Composite Cementitious Materials and High Performance Admixtures in High Performance Shotcrete

In this paper, the influence of liquid alkali-free accelerator and advanced composite cementitious materials on the mechanical properties, durability and workability of shotcrete was studied. The important role of the two materials in the performance improvement of shotcrete was clarified. The technical measures proposed were verified by field test. The results show that: In terms of workability, the composite use of alkali-free accelerator and functional admixture can achieve fast setting and high early strength of shotcrete, thus effectively reducing the rebound rate; In terms of mechanical properties, functional admixture can effectively improve the early mechanical properties of shotcrete, while alkali-free accelerator can ensure the long-term development of mechanical properties; In terms of durability, the use of functional admixtures can effectively improve the compactness of shotcrete, and the test results of 56d electric flux are lower than 1000C.

EFFECT OF LIMESTONE POWDER ON THE PROPERTIES OF BLENDED РORTLAND CEMENTS

The article shows the relation between sustainability and cement manufacture that can be obtained by the replacement of clinker with limestone additive. This decreases the use of energy resources and reduces CO2 emissions in cement production. The issue of partial Portland cement clinker substitution by finely ground limestone in the production of market-oriented types of cement type CEM II is solved on the cement plant PJSC "Ivano-Frankivsk Cement". The indexes of physical-mechanical tests of certified Portland limestone cement with high early strength CEM II/A-LL 42.5 R produced by PJSC "Ivano-Frankivsk Cement" are given. Finely dispersed limestone in Portland-composite cements with slag promotes a more complete synergic effect. It is established, that rapid-hardening blended Portland cements with limestone powder provide technological, technical, ecological, and economic effects in the production of prefabricated and monolithic reinforced concrete.

EFFECTS OF COLD JOINT AND ITS DIRECTION ON THE COMPRESSIVE AND FLEXURAL STRENGTH OF CONCRETE

A cold joint is the main problem in concrete construction, especially in large quantities such as mass concrete. The capacity of mixing plan and manpower make monolith casting is impossible. The distance between the batching plant and the construction location is also an obstacle to cold joints. This study would test the compressive and flexural strength due to the effect of cold joint in concrete. The period of the casting between two concrete (cold joint) was 120 minutes and 240 minutes. Tests carried out in the form of compressive strength and flexural strength of the vertical and horizontal directions of cold joints. The types of concrete used in this study include normal concrete with 35 MPa compressive strength, concrete with high initial compressive strength using superplasticizer, and concrete using polypropylene fiber as added material. Compressive and flexural strength tests were carried out at 3, 7, 14 and 28 days. All specimens used water curing up to the predetermined test life. The test results show that specimen with the cold joint connection in normal concrete has a decrease in quality (flexural and compressive), so does with the concrete with superplasticizer (high early compressive strength), whereas in concrete using fiber has increased in strength compared to normal concrete without cold joint connection.

Steel fibrous concrete with high-early strength for rigid pavements repair

Experimental results, including the selection of repair concrete and steel-fiber-concrete mixtures for rigid pavement repair are presented. The complex effect of the superplasticizer, hardening accelerating agent and steel anchor fiber on the concrete mixture properties has been studied. Compressive and flexural strength characteristics of the repair material were determined in the early and design ages of hardening. Using the method of experimental statistical modeling, the optimal dosages of dispersed reinforcement in combination with accelerating agent and workability modifier have been determined.

Enhanced toughness of ultra-fine sulphoaluminate cement-based hybrid grouting materials by incorporating in-situ polymerization of acrylamide

Deep coal mining requires grouting reinforcement materials with adjustable setting time, high early strength and toughness. Sulphoaluminate cement-based grouting materials (SCGM) have been widely used due to their low cost, but still suffer from poor deformation and toughness. To solve this problem, in-situ polymerization of acrylamide was developed to modify SCGM, and the effects of acrylamide addition on the fluidity, setting time, mechanical properties, and microstructure evolution of SCGM were systematically investigated. The results indicated that the addition of acrylamide significantly improved the toughness of SCGM. When the acrylamide content reached 35 wt%, the flexural strength of SCGM increased to 10 MPa and the compressive strength reached 35 MPa. In light of microstructural analysis, the exothermic heat of SCGM hydration promoted the free radical polymerization of acrylamide to form inorganic–organic hybrid grouting material with a three-dimensional interpenetrating network structure, which was responsible for the enhanced toughness of SCGM. Those results provided a new method to enhance the toughness of SCGM, making it more suitable for grouting reinforcement engineering.

Water stability of bonding properties between nano-Fe2O3-modified magnesium-phosphate-cement mortar and steel fibre

Magnesium phosphate cement (MPC) presents high early strength, fast setting and hardening, excellent bonding performance, and good corrosion and freezing resistance. The excellent performance of MPC enables it to have a wide range of potential applications. However, the brittleness and poor water stability limit its wide application. Incorporating fibres into MPC is a common toughening method, and the bonding between MPC and fibre has a significant impact on the toughening effect. In this paper, effects of the amount of nano-Fe2O3 (NF) and water immersion time on the bonding properties between steel fibre and MPC mortar (MPCM) were investigated using fibre pull-out, compressive, and splitting tensile tests and microstructure analysis. Incorporating NF significantly improved the bonding strength and pull-out energy between steel fibre and MPCM after water immersion. The optimal content of NF was 2 vol%. New hydration products (such as dense iron phosphate) and the compact structure formed with the addition of NF inhibited the interfacial cracks that result from water immersion. This research is very beneficial for construction project applications of fibre-reinforced MPCM in watery environments.

Ecofriendly geopolymer concrete: a comprehensive review

After ordinary Portland cement (OPC) concrete, geopolymer concrete (GPC) is the most advanced form of concrete. GPC has many advantages including improved strength and durability properties. High early age strength and ambient curing of GPC helps to reduce the construction time. Factors such as binder materials, alkali-activated solution, and curing methods control GPC’s strength properties. Moreover, when industrial byproducts such as fly ash and ground granulated blast-furnace slag (GGBS) are added to GPC, this leads to advantages such as reduced carbon dioxide emission, ability to reuse of waste materials, thus saving valuable lands from getting converted into dump yards, cost reduction, and so on. Moreover, the energy required for the extraction of raw materials is also reduced. In this paper, GPC’s strength and durability characteristics, its mix design procedure, its effect of fibers on mechanical properties, and its structural performance are comprehensively reviewed. Moreover, the development of high-strength GPC using fly ash with sodium hydroxide as an alkaline solution under oven curing condition is highlighted. To develop GPC from different binder materials, trial and error methods are proposed. Rangan’s mix design procedure is used for fly ash-based GPC. Moreover, the inclusion of fibers, it was found, improves the ductile nature of GPC. Suggestions and scope for future GPC-related research are also included.

EXPERIMENTAL AND ANALYTICAL STUDY OF A NEW KIND OF STEEL-PVA HYBRID FIBER CONCRETE IN THE ANCHORAGE ZONE OF A BRIDGE EXPANSION AND CONTRACTION INSTALLATION

In this paper, a new kind of steel-polyvinyl alcohol (PVA) hybrid fiber concrete with high early strength and better road performance is proposed for use in the anchorage zone of a bridge expansion and contraction installation (BECI). Firstly, a comprehensive test design method is adopted to evaluate the mechanical properties of the concrete by adding different percentages of fibers, and the optimal percentages of steel and PVA fiber additives are determined. The results of the compressive and flexural strength test indicated that the concrete with added 1.5 % steel fiber and 0.12 % PVA fiber has a higher early strength. Secondly, to evaluate the performance of the improved concrete, the finite-element method was adopted to model the anchorage zone concrete of the BECI, and the loading location of maximum stress was determined and some factors, such as overload and horizontal force coefficient, were considered. The maximum stresses of the anchorage zone are less than the ultimate stresses of the steel-PVA hybrid fiber concrete. It can be concluded that the improved concrete has better road performance. Finally, a case study of the actual bridge was carried out to verify the practical value of the steel-PVA hybrid fiber concrete. Although there is some reduction in the compressive strength, the new concrete is more suitable than the conventional concrete to meet the requirements for the construction of concrete in the anchorage zone of the BECI, which can reduce the construction period and show great practical application value.

Influencing mechanism of mineral admixtures on rheological properties of fresh magnesium phosphate cement

Magnesium phosphate cement (MPC) has been used as grouting materials with unique advantages of quick setting and high early strength. The rheological properties (RPs) of MPC, being vitally crucial for site operation, need to be studied further. This study added fly ash (FA) and silica fume (SF) into MPC to prepare MPC-FA and MPC-SF pastes, and the RPs were measured. The influencing mechanisms of FA and SF on the RPs were studied by measuring the zeta potential, hydration heat, 1H nuclear magnetic resonance (NMR) relaxation signal, water film thickness, and mineral changes. Experimental results indicate that the rheological parameters can also be analyzed by using the Bingham model. FA and SF increase the yield stress (τ0), but they have different effects on plastic viscosity (η). The η value increases remarkably with an increased FA content, and it decreases slightly when increasing the SF content. The mechanisms of FA and SF on RPs of MPC can be explained from three aspects, i.e., hydration process, water film thickness and zeta potential. FA accelerates the hydration and makes the inflection points of 1H NMR relaxation signal sharply ahead of schedule. The decrease in free water reduces the water film thickness among solid particles correspondingly. Likewise, the presence of FA decreases the zeta potential value significantly. Hydration is the most important factor for the rheological behavior of MPC paste, followed by the separation distance of the particles and followed by the surface charge.

Effect of Calcium Nitrate on the Properties of Portland-Limestone Cement-Based Concrete Cured at Low Temperature.

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cement.

Mix design and rheological properties of magnesium potassium phosphate cement composites based on the 3D printing extrusion system

The magnesium potassium phosphate cement composites (MPCCs) with rapid setting, high early strength and low shrinkage performances show considerable potential for 3D printing. In this study, the synergistic effects of magnesium to phosphate (M/P) mass ratio, borax content and fly ash content on the the initial setting time and rheological properties of 3D printed MPCCs (3DP-MPCCs) were investigated using response surface methodology (RSM). The dynamic yielding behaviours are obtained based on Herschel-Bulkley model. The effects of mix design on deformation rate and compressive strength of 3DP-MPCCs were discussed. The results showed that the initial setting time of 3DP-MPCCs was prolonged to 30 min to 90 min by optimizing the mix design and decreased with the increase of M/P mass ratio. The incorporation of borax significantly reduced the consistency factor, which was beneficial to the extrudability of 3DP-MPCCs. High M/P mass ratio was the critical factor for the better buildability of 3DP-MPCCs, which can be further improved by increasing the FA content. Finally, the 3DP-MPCCs with M/P mass ratio of 3.0, 40% borax and 25% FA was determined as the optimal mix design, showing the minimum deformation rate of 0.28% and highest compressive strength of 32.59 MPa, respectively.

Lightweight concretes based on wheat husk and hemp hurd as bio-aggregates and modified magnesium oxysulfate binder: Microstructure and technological performances

Using lightweight building materials from ecological resources reduces the environmental impact of buildings. Most attention has been paid to lime-based agro-concretes, but low binder-aggregate compatibility as well as slow strength gain are drawbacks. The use of magnesia-based binders has the potential to mitigate these problems. Here, a modified magnesium oxysulfate (MOS) cement was used to manufacture lightweight concretes using wheat husk, a highly available and unexploited resource, and hemp hurd as bio-aggregate. A combined microstructural-technological study was performed, filling gaps in existing literature. Through microstructural observations made by X-ray Powder Diffraction, microscopy imaging (optical, electron) and mercury porosimetry, mechanical and thermal properties in the different concretes were elucidated. It will be shown that the developed lightweight concretes are technologically competitive with lime-based ones, having the advantage of possessing high early strength.