Compressive Strength Of Cementitious Materials Research Articles

Preparation and characterization of cementitious materials from dedioxinized and dechlorinated municipal solid waste incineration fly ash and blast furnace slag

To address the resource utilization issue of MSWI fly ash, a method has been proposed to prepare cementitious materials using harmlessly processed MSWI fly ash (HPFA). After washing and thermal treatment, The physicochemical properties of HPFA were characterized using QXRD, ICP, XRF, and GC-MS. Cementitious materials were prepared using HPFA, gypsum and blast furnace slag (BFS) as raw materials, Through XRD, TG, FTIR, TEM, and SEM-EDS methods, the hydration and hardening characteristics were investigated, and the leaching of heavy metals from solidified materials in simulated surface water and landfill environments was evaluated using ICP-MS. The results indicate that the harmless treatment can effectively reduce the chloride content and dioxins in MSWI FA but still contains heavy metals. The addition of HPFA (10%-50%) can enhance the compressive strength of cementitious materials, accelerate the exothermic process of cement hydration, and increase the total heat release of hydration, implying an improvement in the degree of hydration of the system.HPFA could effectively promote the hydration of gypsum and BFS, resulting in the higher formation of ettringite and C-(A)-S-H（C/S=1，Al/Si=0.3）.The formation of C(Mg/Fe)-(A)-S-H suggests that the Fe-Mg solid solution phase in HPFA may have participated in the hydration reaction. The increased stability of highly cross-linked (Q4) silicate tetrahedral structure with time implies that the material may have good durability. The leaching amount of heavy metals met the standards of Class I surface water in GB3838–2002 and GB5085.3–2007 which implies that the material has environmental safety. This study innovatively provides a preparation path for harmless MSWI fly ash and cementitious material ratios, reveals the hydration mechanism of HPFA in cementitious materials, evaluates the solidification ability of heavy metals, and provides important ideas for the resource utilization of MSWI fly ash.

Experimental Study on the Properties and Hydration Mechanism of Gypsum-Based Composite Cementitious Materials

In order to achieve the resourceful, large-scale and high-value utilization of bulk industrial solid wastes such as flue gas desulfurization gypsum (FGDG), fly ash (FA) and ground blast furnace slag (GGBS), and to reduce the dosage of cementitious materials, orthogonal experimental methods were used to prepare composite cementitious materials based on the principle of synergistic coupling and reconstruction of multi-solid wastes. Through the method of extreme difference and ANOVA, the influence law of different factor levels on the performance of the cementitious materials was studied, and the maximum compressive strength of cementitious materials was reached when the ordinary Portland cement (OPC) dosage was 20%, the FGDG dosage was 56%, the FA dosage was 19.2% and the slag dosage was 4.8%, and the W/B was 0.55. The hydration products and microscopic morphology of the cementitious materials were analyzed by means of XRD, SEM and MIP techniques, so as to elucidate the complex synergistic hydration mechanism, and then to determine the more optimal group distribution ratio. The results show that the hydration reaction between FGDG and OPC can be synergistic with each other, and C-A-H further generates AFt under the action of SO42−, and at the same time, it plays the role of alkali-salt joint excitation for FA–GGBS, generates a large amount of cementitious materials, fills up the pores of the gypsum crystal structure, and forms a dense microstructure.

Effect of Glycine on the Wet Carbonation of Steel Slag Used as a Cementitious Material.

The wet carbonation process of steel slag (SS) is envisaged to be an effective way to sequestrate CO2 and improve the properties of SS as a supplementary cementitious material. However, the carbonation process still struggles with having a low carbonation efficiency. This paper studied the effect of glycine on the accelerated carbonation of SS. The phase composition change of carbonated SS was analyzed via XRD, FT-IR, and TG-DTG. The carbonation process of SS is facilitated by the assistance of glycine, with which the carbonation degree is increased. After 60 min of carbonation, SS with glycine obtained a CO2 sequestration rate of 9.42%. Meanwhile, the carbonation reaction could decrease the content of free calcium oxide in SS. This significantly improves the soundness of SS-cement cementitious material, and the compressive strength of cementitious materials that contain carbonated SS with glycine is improved. Additionally, the cycling performance of glycine in the successive wet carbonation process of SS was investigated. Multicycle experiments via solvent recovery demonstrated that although the promotion effect of glycine was reduced after each cycle, compared with the SS-water system, the carbonation process could still be facilitated, demonstrating that successive wet carbonation via solvent recovery has considerable potential. Herein, we provide a new idea to facilitate the wet carbonation process of SS and improve the properties of SS-cement cementitious material.

Application of electrical resistivity for estimating compressive strength of FRC at early-ages

ABSTRACT The addition of fibers improves the ductility and compressive strength of concrete. Utilizing fiber in concrete, on the other hand, alter the electrical conductivity of concrete and that is especially important when concrete is being used in applications that electrical resistivity of concrete has been taken into account in the design process. Electrical resistivity of concrete can be measured using nondestructive testing techniques. Electrical resistivity has been proven to be in relationship with compressive strength of cementitious materials. The link between surface electrical resistivity (ER) and compressive strength (CS) of FRC at early ages has been investigated in the current study. Twenty-one distinct FRC mixtures have been cast using various fiber types, w/c ratios and fiber volume fractions. Test results have shown a strong relationship between electrical resistivity and mechanical properties of fiber reinforced concrete. A novel empirical equation has been proposed to estimate the compressive strength of early-age fiber reinforced concrete. The adequacy of this equation was determined by comparing actual and projected compressive strength values for FRC using a coefficient of variation. The early-age compressive strength of FRC was found to be reliable when the proposed equations were utilized.

Exploring macroscopic and microscopic impacts of alcohol amine modified with water-reducing agent on cementitious material and its application

In order to meet function requirements of slope protection and ecology for grass-planting concrete with a random porous structure, this study proposes two typical alcohol amines, namely, water-reducing agent modified triethanolamine (TEA) and diethanol monoisopropanolamine (DEIPA), as admixtures for the production of grass-planting concrete. The crystal structures, elemental ratios, and hydration products of cementitious materials with modified alcohol amines were investigated to explore their mechanism of action, reinforcement, and appropriate dosage. The compressive strength of cementitious materials and the spread of mortar made from modified alcohol amines were investigated to evaluate their impact on the compressive strength and workability of grass-planting concrete. The results show that modified TEA can more uniformly reduce the calcium-silicon ratio of the hydration products, leading to enhanced crystallization and densification at a dosage of 0.08%. At a dosage of 0.16%, modified DEIPA can effectively promote the hydration of tricalcium silicate and the secondary hydration of generated calcium hydroxide. The reduction in calcium hydroxide content resulted in an increase in strength. Both these amines enhance the bonding ability of cementitious materials. The spread of the modified cementitious materials is further improved, and suitable cementitious materials with a low water-cement ratio can be obtained for making grass-planting concrete to create uniformly wrapping coarse aggregates with the cementitious material. Modified TEA and modified DEIPA significantly increased the 28-day compressive strength of cementitious material by more than 104%, and the improvement effect of modified DEIPA was significantly better than that of modified TEA. The modified alcohol amines show great potential for practical application in production.

Study on properties and mechanism of alkali-activated geopolymer cementitious materials of marble waste powder

In order to explore the effect and mechanism of marble waste powder on the properties of alkali-activated slag composite cementitious materials. The effects of different parameters on the properties of alkali-activated slag composite cementitious materials were studied by taking the particle size, content of marble waste powder and alkali liquid modulus as the change parameters. The results show that marble powder (SW) can effectively improve the fluidity of the slurry, and the larger the particle size, the more obvious the fluidity of the slurry. The alkali liquid modulus has a significant effect on the compressive strength of cementitious materials, and low alkali liquid modulus is beneficial to improve the compressive strength of cementitious materials. Alkali-activated marble powder cementitious material found Ca6(Si2O7)(OH)6 and Ca(OH)2, and Si–O bond vibration characteristic peak vibration peak in geopolymer unit. Based on the experimental results, the mechanism and reaction process of marble powder were established.

Preparation and Mechanical Properties of Low Carbon Cementitious Materials with Superfine Cement Reverse Filling High-Volume Mineral Admixtures.

In order to increase the content of mineral admixtures in cement, this study proposes a method for preparing a high-volume mineral admixture cementitious material (HMAC) using superfine cement as a reverse filling material. Firstly, superfine cement is prepared through mechanical grinding. Then, the activity of mineral admixtures (such as slag and fly ash) is enhanced by mechanical grinding, sulfate activation, and alkali activation methods. Meanwhile, the evolution of HMCM from microstructure to macroscopic mechanical behavior is studied by combining a laser particle size analyzer and a scanning electron microscope. Furthermore, the reverse filling mechanism of superfine cement on mineral admixtures under different activation conditions is proposed. Results show that superfine cement can largely improve the utilization rate of cement clinker and the compressive strength of cementitious materials. In the condition that the compressive strength is not lower than that of the control group (without mineral admixture), the content of mineral admixture can be increased to 50%, 70%, and 90% after mechanical grinding, sulfate activation, and alkali activation, respectively. Analysis indicates that the reverse filling effect of superfine cement is the main reason for improving the density of the HMCM.

Recycling glass fibers from thermoset epoxy composites by in situ oxonium-type polyionic liquid formation and naphthalene-containing superplasticizer synthesis with the degradation solution of the epoxy resin

Glass fibre-reinforced thermoset (GFRT) epoxy composites with permanent cross-linked polymer networks are difficult to recycle, leading to the production of large amounts of waste. Developing an efficient approach to reuse both the high-value fibre and the resin matrices is thus imperative. In this work, we explored the application of H2SO4 (98%) to react with ether and benzene groups in the epoxy backbone at room temperature. As a result, a new family of poly(ionic liquid)s (PILs) comprising cationic oxonium was produced. The in situ oxonium PIL formation enables clean glass fibres to be released with well-maintained surface microscopic morphology, chemical structure and tensile modulus close to the virgin glass fibres (vGFs). Furthermore, the dissolved matrix solution functions as a synergistic sulfonation agent in the synthesis of naphthalene containing superplasticizer. The obtained additive is superior to the fresh H2SO4 sulfonated naphthalene formaldehyde condensate (SNF) in reducing water content (33% vs 19%) and improving compressive strength of cementitious materials by 29%. Therefore, this novel eco-friendly strategy provides an open-loop solution for GFRT composites recycling at ambient conditions producing no new waste.

Solidification of heavy metals in lead smelting slag and development of cementitious materials

Lead smelting slag (LSS) is a hazardous waste containing heavy metals (Cr, Ni, Cu, Zn, As, and Pb) and its improper disposal may cause irreparable damage to the ecosystem. Cementitious materials prepared with LSS can be used in construction fields and hazardous heavy metals are also solidified in prepared cementitious materials. In this study, the effects of particle sizes of LSS (8.30, 12.54, and 19.04 μm) on the compressive strength of prepared with high-volume LSS multiple coupling excitation cementitious materials were explored. According to the composition of LSS, activators were set as 6% MgO, 6% bischofite, 7% CaO, 1% CaCl2, and 8% cement, respectively. Decreasing the particle size of LSS could significantly improve the compressive strength of cementitious materials, especially in the early stage. The sample containing LSS with the particle size of 8.30 μm showed the highest compressive strength (47.1 MPa) and activity index (78.2%) among the samples containing LSS with different particle sizes. LSS with three particle sizes was analyzed with Fourier transform infrared spectroscope (FTIR) and X-ray diffractometer (XRD). The analysis results indicated that decreasing the particle size of LSS increased the specific surface areas (SSAs) and decreased the degree of crystallinity . Moreover, the microscopic analysis of cementitious materials implied that decreasing the particle size enhanced the degree of reaction and gelation , thus resulting in the denser structure of blocks. The results confirmed the compressive strength of LSS-based cementitious materials. • Heavy metals in LSS were effectively solidified in cementitious materials. • A hydration model for LSS-based cementitious materials is proposed. • The paper presents early strength could be significantly improved with decreasing particle size. • LSS-based cementitious materials can be used in the field of prefabricated construction industrial.

Effect of seawater on the workability, adsorption, dispersion and compressive strength of cementitious materials incorporated with polycarboxylate superplasticiser

The shortage of fresh water obviously limits the development of the construction industry. The aim of this study is to investigate the possibility of using seawater in building concrete. The effect of seawater on the workability, adsorption, dispersion and the compressive strength of cement pastes incorporated with two types of polycarboxylate superplasticisers (PCE) was studied. In addition to examining minislump and compressive strength, water film thickness, adsorption amount and adsorption layer thickness were investigated as well to explore the mechanism. The results showed that, compared to tapwater (TW), the minislump of PCE incorporated cement paste was reduced by mixing it with seawater (SW). Moreover, although the seawater increased the compressive strength of cement paste without PCE, the addition of PCEs reduced the compressive strength of cement pastes mixed with both TW and SW. The replacement of SW to TW increased the adsorption amount and while it reduced the thickness of adsorption layer and water film.

Effects of Nano-CSH on the hydration process and mechanical property of cementitious materials

Nanomaterials are widely used in cement to improve the various properties of cement-based materials. Nano-CSH is considered as an effective accelerator for the hydration of cement. This paper studied the effects of nano-CSH on the hydration behavior and compressive strength of cementitious materials with various mineral admixtures. Isothermal calorimetry test was used to study the early hydration of cement paste. Thermogravimetric and X-ray diffraction tests were used to study the evolution of hydration product and unhydrated mineral phases in the hydrated cement paste. The presentation of compressive strength can evaluate the influence of nano-CSH on the property of cement-based material at the macro level. The obtained results show that the used nano-CSH can promote the hydration of tricalcium silicate (C3S), and is more active on the hydration of tricalcium aluminate (C3A) in the samples with GGBFS. The presence of nano-CSH can definitely accelerate the secondary hydration reaction of mineral admixtures.

The impact of carboxylic acid type hydrophobic agent on compressive strength of cementitious materials

One of the most effective methods to improve durability of cementious materials is resist the intrusion of water born aggressives by mixing with hydrophobic agent, limiting the development of compressive strength. In this study, effect of carboxylic acid ammonium salt hydrophobic agent on compressive strength of cementitious materials is examined and its mechanism is analyzed. It is investigated that the impact of hydrophobic agent on hydration degree, amount and structure of hydration products shows that hydrophobic agent has little influence on hydration and products. In contrast, the generation of calcium carboxylate and increase of air content will cause loose of the microstructure of cement pastes confirmed by electrical conductivity and zeta potential. The secondary stress is proposed to analyze the effect of microstructure change on the compressive strength. The result of this study shows that hydrophobic agent might have great sense to improve durability of concrete and the compressive strength reduction should be considered.

Comparison of Microbially Induced Healing Solutions for Crack Repairs of Cement-Based Infrastructure

Reinforced concrete crack repair and maintenance costs are around 84% to 125% higher than construction costs, which emphasises the need to increase the infrastructure service life. Prolongation of the designed service life of concrete structures can have significant economic and ecological benefits by minimising the maintenance actions and related increase of carbon and energy expenditure, making it more sustainable. Different mechanisms such as diffusion, permeation and capillary action are responsible for the transport of fluids inside the concrete, which can impact on the structure service life. This paper presents data on microbially induced repair and self-healing solutions for cementitious materials available in the contemporary literature and compares results of compressive strength test and capillary water absorption test, which are relevant to their sealing and mechanical characteristics. The results of the repair and self-healing solutions (relative to unassisted recovery processes) were “normalized.” Externally applied bacteria-based solutions can improve the compressive strength of cementitious materials from 13% to 27%. The internal solution based solely on bacterial suspension had 19% improvement efficacy. Results also show that “hybrid” solutions, based on both bio-based and non-bio-based components, whether externally or internally applied, have the potential for best repair results, synergistically combining their benefits.

Electrolytic manganese residue-based cement for manganese ore pit backfilling: Performance and mechanism

Slag backfilling with electrolytic manganese residue (EMR) is an economical and environmentally-friendly method. However, high ammonium-nitrogen and manganese ions in EMRs limit this practice. In this study, a method of highly efficient simultaneous stabilization/solidification of ultrafine EMR by making EMR-based cementitious material (named EMR-P) was proposed and tested via single-factor and response surface optimization experiments. Results show that the stabilization efficiency of NH4+ and Mn2+ were above 95%, and the unconfined compressive strength of the EMR-P was 18.85 MPa (megapascal = N/mm2). The mechanistic study concluded that the soluble manganese sulfate and ammonium sulfate in EMR were converted into the insoluble precipitates of manganite (MnOOH), gypsum (CaSO4), MnNH4PO4·H2O, and struvite (MgNH4PO4∙6 H2O), leading to the stabilization of NH4+ and Mn2+ in the EMR-P. Leaching tests of EMR-P indicated that NH4+, Mn2+, and others heavy metals in the leachate were within the permitted level of the GB/T8978-1996. The novelty of this study includes the addition of phosphate and magnesium ions to precipitate ammonium-nitrogen and the combination between calcium ions (from CaHPO4∙2 H2O) and sulfate (from the EMR) to form calcium sulfate to improve the stability and unconfined compressive strength of cementitious materials (EMR-P).

Quantitative relationship between pore size distribution and compressive strength of cementitious materials

Cementitious materials have complex pore structure, which has a significant impact on material properties. The present paper aims to determine the quantitative relationship between pore size distribution and compressive strength of cementitious materials. An influence function is proposed to describe the influence of pore size on strength, based on which an integral model of compressive strength is established. A total of 11 sets of mortar specimens with wide differences in pore size distribution were prepared with the virtual pore method to verify the influence function and the strength model. The influence function indicates that the effect of pores per unit volume on strength increases with the increase of pore size. The effect increases slowly at small pore size and increases significantly at large pore size like microscale pores. The influence of porosity on strength can be determined quantitatively with the proposed influence function when the pore size distribution is obtained, which further gives the predicted strength. It is indicated that microscale pores have a significant impact on the material strength, so the existence of these pores should be avoided to improve material strength.

Statistical analysis of acoustic emissions generated during unconfined uniaxial compression of cementitious materials

The article reports a study on the ‘goodness of fit’ of Weibull and Normal (Gaussian) distributions on the compressive strength and the corresponding Acoustic Emissions (AE) of cementitious materials. An attempt has been made to understand the variation of the parameters of the Weibull distribution and the Gaussian distribution carried out on the uniaxial compressive strength data and the corresponding recorded AE parameters. The statistical analysis of ‘Damage Parameter’ based on the peak amplitude of AE signals was also carried out. It was observed that the Weibull distribution was a better fit than Gaussian distribution for compressive strength and damage parameter. But in the case of AE parameters, Gaussian distribution was a better fit. The results obtained from this statistical study may be an addition to the existing knowledge on the statistical approach of AE associated with cementitious materials. A statistical approach may be suitable in predicting the data values without conducting further experiments. The results may be useful to understand the variation of physical properties such as homogeneity and ductility with the variation of compressive strength of cementitious materials and its corresponding AE parameters.

Effect of cement strength class on the generalization of Abrams' law

Abrams' law is used to predict the compressive strength of cementitious materials based on water/cement ratio (W/C). While compressive strength does not only depend on W/C, but also there are many factors that influence the strength of mortar, such as cement strength class and sand/cement ratio (S/C). Novelty of this study, the effect of three types of cement strength classes in 54 cement mortar mix designs on generalization of modified Abrams' law and Bolomey's formula are investigated. Modified equations base on cement strength class and S/C were proposed for the compressive and flexural strength of cement mortar in the range between a very low W/C and a very high W/C. The results showed that the modified equations additional to W/C are strongly influenced by the cement strength class and S/C. Moreover, to show sensitivity of above parameters microstructural characteristics were also studied by the scanning electron microscope (SEM) and an energy dispersive spectrometer analysis (EDS).

Statistical modelling of compressive strength controlled by porosity and pore size distribution for cementitious materials

The compressive strength of cementitious materials is significantly affected by its pore system inherent in the matrix of cement paste, not only porosity but also pore size distribution. In present work, by deconvolution analysis, the total pore size distribution of cement paste is represented by a multiple distribution consisting of two single distributions for the capillary pores and the macro pores respectively. In this way, the widely accepted Raleigh-Ritz (R-R) function is challenged and the lognormal distribution is found to be best to approximate the pore size distribution for cementitious materials. With pore size distributions, a statistical model based on probability principle and fracture criterion is proposed to reveal the physical mechanism of reduction in compressive strength induced by porous structures. Parameters in the model, e.g. fracture toughness of cement paste matrix, fracture mode, volume of specimen, porosity and pore size distributions, are further discussed and examined quantitatively.

Mechanical Properties of Self-Healing System in Cementitious Material with Microcapsule

In this paper, several urea–formaldehyde/epoxy microcapsules with different particle sizes were synthesized by in-situ polymerization. The chemical structure and compressive rupture load of microcapsule were characterized. The effect of microcapsule dosage, particle size and preload pressure on compressive strength of cementitious materials was studied. The result shows: when the particle size of microcapsule is 2 mm~2.5 mm, the rupture load of microcapsule is highest, more than 3N; When the microcapsule dosage is less than 2.5%, the strength loss of the matrix is relatively small; With the increase of the particle size of the capsule, the strength of the matrix decrease greatly; When the dosage of microcapsule is 2.5%, the particle size is 1.5 mm and the preload pressure is 30%~45%fmax, the compressive strength of the self-healing specimen is 8% higher than that of the non-preloaded specimens, which shows a certain self-healing performance.

Estimating the mechanical properties of hydrating blended cementitious materials: An investigation based on micromechanics

The hydration model of Parrot & Killoh (1984) has been extended to blended cements and coupled to a micromechanical scheme similar to that of Pichler & Hellmich (2011) to estimate the Young modulus and the compressive strength of cementitious materials as a function of time. A finite aspect ratio of 7 is introduced to describe the shape of the hydrates and improve the estimate of the early age strength by the micromechanical scheme. Furthermore, accounting for the stress fluctuations in the cement paste partly explains the fact that the compressive strength of a concrete can be lower than that of its cement paste. Finally, the estimated physical properties are compared to numerous experimental measurements from the literature and new experimental measurements on blended cement pastes featuring significant weight fractions of limestone filler, fly ash or silica fume. It is shown that the present model slightly overestimates the dilution effect.