Binary Cementitious Materials Research Articles

Investigation on the compressive strength of desulfurization gypsum binary cementitious materials with low energy consumption: the utilization enhancement of industrial wastes

Geopolymer, a new low carbon green cementing binder, has widely been used as an alternative to Ordinary Portland cement (OPC), which effectively reduces carbon emissions and industrial solid waste stockpiles on land, also improving solid waste utilization. To raise the utilization of sulphate solid waste and decrease energy consumption, desulphurization gypsum (DG)-based binary cementitious materials were synthesized, and the effects of DG dosage and alkali exciter components on the compressive strength of binary cementitious materials were investigated. In addition, the improvement mechanism of the mechanical properties of binary cementitious materials was revealed by microstructure characterization tools. The results prove that the optimum compressive strength of 52.5 ± 0.5MPa is achieved with a DG dosage of 20%, SiO2/Na2O of 1, water glass dosage of 10% and water-cement ratio of 0.5. Due to the continuous reaction of sulphate in DG with Ca2+ and reactive silicates/aluminosilicates during the curing process, the crystals of ettringite (AFt) are generated and filled the pores of binary cementitious materials and thus furtherly enhancing its compressive strength. And the gel products wrap the AFt that has been filled in the inter-vacancy space on the surface of aluminosilicates already formed at an earlier stage. In summary, ground granulated blast-furnace slag (GGBS) and DG work synergistically to reduce the negative effects of delayed AFt and increase the compressive strength of the geopolymer.

Hydration Characteristics and Mechanical Properties of Cement-Based Materials Modified by Calcined Zeolite and Montmorillonite

Montmorillonite and clinoptilolite zeolite were used as representative materials to prepare calcined clay-cement binary cementitious materials in order to study the effect of calcination treatment on the activation of clay minerals and the activity difference between layered and framed clays in this research. The influence of different calcined clay content (2%, 4%, 6%, 8%, 10%) on the fluidity, compressive strength, microstructure, phase change, and hydration heat of cement-based materials were analyzed. The calcined clay improves the fluidity of cement-based materials as compared with the uncalcined group. The addition of calcined montmorillonite (CMT) improves the development of mechanical strength, and the optimal compressive strength reaches 85 MPa at 28 days with 8% CMT. However, the activity of calcined clinoptilolite zeolite (CZL) is weak with few reaction sites, which slightly reduced the mechanical strength as compared to the blank sample. The addition of CMT changes the microscopic morphology of hydration products such as C-S-H and C-A-H, leading to the formation and transformation of ettringite in the early stage. It promotes the gradual polymerization of Si-O bonds into SiO-Si bonds simultaneously, which accelerates the early hydration process. However, CZL acts mainly as a filling function in the cementitious system. In brief, CMT as an admixture can improve the mechanical properties of cement, but CZL has little effect. This work provides a guideline for the applications of calcined clay in cement, considering the influence of clay type on workability and mechanical strength.

Utilization of Corn Cobs Ash as Cementitious and Binary Cementitious Materials in Concrete and Cement-based Composites: A Review

This paper reviews the utilization of corn cobs ash (CCA) as pozzolanic, cementitious, and binary cementitious materials in concrete. CCA is the grey-to-brown, inorganic or heterogeneous residual material derived from the high- temperature incineration or combustion of corn cobs (CC). Despite the typical problematic nature of biomass ash, the chemical composition of CCA renders it a potential pozzolanic material. Therefore, numerous studies have critically examined the process technologies and operational conditions for CCA production and its application as a partial replacement for cement in concrete. Other studies have extensively characterized the physicochemical, morphological, microstructure, and thermal properties of CCA through various analytical techniques. Potential pozzolanic materials must meet the condition: SiO2 + Al2O3 + Fe2O3 ≥ 70%, according to ASTM C618, to which CCA complies satisfactorily. Hence, the use of CCA as a replacement for cement has been investigated over the years. Findings indicate that the partial replacement of cement with CCA decreases compressive strength, thermal conductivity, ultrasonic pulse velocity, and density of the hardened concrete at normal temperatures. Nevertheless, the thermal treatment (calcination) of CCA and extended curing enhances compressive strength owing to higher silica content and extended surface area. Besides, the partial replacement of cement with CCA enhances the insulation properties of mortar, which improves thermal comfort, costs and energy savings in buildings. Hence, the partial replacement of cement with CCA provides an environmentally friendly, low cost, and sustainable approach for valorizing CC residues whilst addressing CO2 emissions in construction.

Investigation on physical properties, strength and phase evolution of binary cementitious materials made of CFBC ash and lime

Circulating fluidized bed combustion ash (CFBC ash) is the wasteof coal-firedcirculating fluidized bed power plant boiler.CFBC ash contains amounts of free limeand anhydrite, which has a self-hardening andexpansion property. This paper studies the influence of CFBC ash fineness and lime or slaked lime dosage on the physical properties, strength and phase evolution of binary cementitious materials (lime or slaked lime-CFBC ash). The experimental results show that when lime or slaked lime dosage is below 30%, throughCFBC ash getting finer, setting timeof binary cementitious materials becomes shorter and compressive strength of that increases, butwater requirement of normal consistency of that decreases to some extent. And when CFBC ash fineness is constant, with the increment of lime dosage, setting timeof binary cementitious materials becomes shorter and water requirement of normal consistency of that increases, butcompressive strength of that declines first and then increases. But when CFBC ash fineness is constant, with the increment of slaked lime dosage, setting timeof binary cementitious materials becomes longer and compressive strength of that declines, butwater requirement of normal consistency of that increases.

Shrinkage-reducing measures and mechanisms analysis for alkali-activated coal gangue-slag mortar at room temperature

By using slag as a calcium source, high-strength alkali-activated coal gangue-slag (AACGS) cementitious material can be prepared. Given that higher drying shrinkage at room temperature is detrimental to the expanded engineering application of the material, this paper studies several methods for reducing drying shrinkage such as shrinkage-reducing admixture (SRA), polypropylene fiber (PPF), sulfate-enriched materials (gypsum, high-performance concrete expansive admixture (HCSA), U-type expansive admixture (UEA)) and water retaining admixture (WRA). Meanwhile, the mechanisms for drying shrinkage compensation were deeply analyzed by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Experimental results show that the addition of admixtures to reduce the drying shrinkage of AACGS mortar is related to the change of pore size of 2–5 nm, and reduces the volume fraction of the minimum aperture. At room temperature, reducing the surface tension of pore solution, generating expansion products, increasing compressive strength and improving pore structure distribution by adding admixtures are important measures to reduce drying shrinkage. SRA exhibits the strongest capacity to compensate for drying shrinkage, followed by UEA, WRA, HCSA, PPF and gypsum. Despite better compensation for drying shrinkage with the increase in SRA dosage, the reduction of strength value becomes more drastic. The findings of this study provide substantial experimental foundations and in-depth theoretical analyses for the drying shrinkage compensation of AACGS binary cementitious materials.

Electrical indication of binary cementitious materials with steel fibres ability to resist the low permeability of concrete

The main objective of this study is to identify the durability properties of the test method, chloride ion penetration and sorptivity test in the combination of waste binding materials (supplementary cementitious materials) along with steel fibre reinforced concrete for various mixes. Most of the prediction methods, how much chloride ion ingress into the concrete and water absorption are mainly related to the long term serviceability of the deterioration of concrete. This laboratory experimental test results for 28, 56, 90 days for the RCPT values 31.54%, 34.26% and 38.16% respectively and 40.68% and 17.98% for 56 and 90 days test results for water absorption based on the test results has striving to produce the better improvement of structural concrete when the addition of slag up to 20% with low calcium fly ash up to 20% along with 1.5% of steel fibres and also addition of RHD up to 9.4 L for 470 kg/m3 of cement (binding materials) along with 1.5% of polycarboxylate ether-based superplasticizer with low w/b ratio of 0.32.

Hydration Kinetics of Portland Cement-Silica Fume Binary System at Low Temperature.

Portland cement–silica fume binary cementitious materials are widely used in engineering construction and have been investigated from micro- to macroscopic aspects. However, the theoretical background on the hydration kinetics of the binary system has not been sufficiently covered in the literature. In this study, the hydration dynamic characteristics of the Portland cement–silica fume binary system curing at low temperature were investigated. Hydration kinetics equations were optimized and a hydration model followed by a computer program was developed to calculate the reaction rate constant K and the reaction order n. This model presented that the hydration process of the binary system at low temperature could be divided into three stages, namely, nucleation and growth (NG), interactions at phase boundaries (I), and diffusion (D). The n values for the binary system varied in the range of 1.2 to 1.6, indicating that the hydration of the binary system at low temperature was a complex elementary reaction. Silica fume can reduce the total heat at the later stage of the hydration and the reaction order n, but increase the heat flow at the accelerating stage and the hydration rate constant K. Low temperature prolonged the hydration induction period, decreased and delayed the secondary exothermic peak, as well as reduced the n and K value.

Hydration of Binary Portland Cement Blends Containing Silica Fume: A Decoupling Method to Estimate Degrees of Hydration and Pozzolanic Reaction

Determination of degrees of hydration/reaction of components of blended cementitious systems (i.e., cement and SCMs: supplementary cementitious materials) is essential to estimate the systems’ properties. Although the best methods for determining degrees of reaction of different SCMs have been recommended by RILEM TC238, they rely on either expensive equipment (e.g., nuclear magnetic resonance) or time-consuming sample preparation and data processing (e.g., backscattered electron image analysis). Furthermore, these methods cannot simultaneously characterize degree of hydration of cement and degree of reaction of SCMs. A novel decoupling method, which can simultaneously estimate the degree of hydration of cement and the degree of reaction of silica fume in binary cementitious materials, is proposed in this study. Based on experimentally determined and theoretically validated stoichiometric parameters of cement hydration and pozzolanic reaction, the contents of calcium hydroxide and hydrate water in pastes are expressed as functions of degree of hydration of cement and degree of reaction of silica fume. With the two contents determined by thermogravimetric analysis, the two degrees can be solved mathematically. It is found that in binary binders the incorporation of silica fume affects hydration kinetics of cement, leading to lower ultimate degree of hydration, shorter dormant stage, and faster hydration in the acceleration stage. As a result, the degree of hydration of cement in blended paste is higher at early ages (e.g., 3 days) but lower at later ages (e.g., 120 days) than that in plain cement paste. In a given blended paste, the degree of reaction of silica fume can be tied to the degree of hydration of cement. The decoupling method is promising for rapid estimations of degrees of hydration/reaction of cementitious materials in a blended system, since it does not require expensive characterization tools or complex data processing methods.

On low-velocity impact response of SIFCON slabs under drop hammer impact loading

The response of thin slabs of Slurry-Infiltrated Fibrous Concrete (SIFCON) with and without reinforcement under low velocity impacts is explored via drop-hammer impact experiments. For comparison purpose, plain cement concrete (PCC) and reinforced cement concrete (RCC) slabs were also cast and tested. To produce SIFCON slabs made with binary cementitious materials, the pre-determined concrete mixtures were designed with 15% of silica fume, 30% of blast furnace as a partial substitute of cement along with a constant 10% of hooked end steel fibres by volume fraction. The replication of a low-velocity impact on slab was achieved by dropping a steel ball (weighing 4.5 kg), with fall height of 457 mm, via the utilization of a self-fabricated drop-hammer impact test device. The parameters like first crack and ultimate failure energy absorption capacity, ultimate crack resistance, crack resistance ratio, ductility indices, and failure pattern were examined. The test results reported that the incorporation of binary blends of silica fume and slag in SIFCON matrix shows better performance in terms of strength and durability characteristics.

Properties of low binder ultra-high performance cementitious composites: Comparison of nanosilica and microsilica

This paper presents the effect of using binary and ternary blends of nanosilica (NS) and microsilica on the mechanical properties of low binder ultra-high performance cementitious composites (UHPCs). For this, two concrete groups were designed with and without silica fume by weight of cement with a constant water/binder ratio and total binder content. Commercially available NS was used in partial substitution of cement at 0%, 0.5%, 1%, 2% and 3% by weight. The results show that among different NS contents, UHPC containing 2% NS exhibited the best results of compressive strength, splitting tensile strength, modulus of elasticity, flexural strengths, load–displacement behavior and fracture energy at 90days. The samples of UHPC containing binary cementitious materials (NS and SF) gave better results than concretes containing only NS. Additionally, the effect of 1% NS is almost equal to that 10% of SF.