The effect of mineral additions based on calcium aluminates on the hydration mechanism of ordinary Portland cement (OPC) was investigated using isothermal calorimetry, thermal analysis, X-ray ...diffraction, scanning electron microscopy, solid state nuclear magnetic resonance and pore solution analysis. Results show that the addition of a calcium sulfoaluminate cement (CSA) to the OPC does not affect the hydration mechanism of alite but controls the aluminate dissolution. In the second blend investigated, a rapid setting cement, the amorphous calcium aluminate reacts very fast to ettringite. The release of aluminum ions strongly retards the hydration of alite but the C–S–H has a similar composition as in OPC with no additional Al to Si substitution. As in CSA–OPC, the aluminate hydration is controlled by the availability of sulfates. The coupling of thermodynamic modeling with the kinetic equations predicts the amount of hydrates and pore solution compositions as a function of time and validates the model in these systems.
•Novel composite-cement technology with anti-microbial co-functionality.•Cetylpyridinium chloride modified montmorillonite (CPC-Mont).•Continuous anti-biofilm activity by gradual CPC release.•No ...reduction in mechanical strength and bonding performance.
The aim of this study was to evaluate the mechanical properties, bonding performance and anti-microbial activity of a novel composite cement containing cetylpyridinium chloride (CPC) modified montmorillonite (‘CPC-Mont’), and using these parameters to determine the optimal particle size and concentration of CPC-Mont the composite cement can be loaded with.
CPC-Mont particles with a median diameter of 30 and 7 µm were prepared and added to a composite cement at a concentration of 2, 3, 4, 5 and 7.5 wt%. Mechanical properties and bonding performance of the experimental composite cements were evaluated by 3-point bending and micro-tensile bond-strength testing. The amount of CPC released from the cement disks was quantified using a UV–vis recording spectrophotometer. The anti-biofilm activity was studied using scanning electron microscopy (SEM).
Adding 30-μm CPC-Mont decreased the mechanical properties and bonding performance of the composite cement, while no reduction was observed for the 7-μm CPC-Mont loaded cement formulation. Although CPC release substantially decreased during the 7-day period assessed, 5- and 7.5-wt% CPC-Mont loaded composite cement inhibited biofilm formation for 30 days.
Loading composite cement with CPC-Mont with a median diameter of 7 µm at concentrations of 5–7.5 wt% was effective in achieving continuous anti-biofilm activity, while maintaining mechanical strength and bonding performance.
•The microstructure development of BCSA cement paste can be characterized by the EIS method.•A modified mathematical equation involving the resistivity is proposed according to the classic equation ...for degree of hydration.•The intrinsic connection between the microstructure and composition transition of hydrated cement pastes with the electrical resistivity is discussed.
In this paper, the interconnectedness among the electrical resistivity, the calorimetric heat and the chemical shrinkage of high Belite calcium sulfoaluminate (BCSA) cement are discussed. Microstructure analyses by using XRD, NMR, ICP-MS and SEM are applied to further demonstrate the relationship among the microstructure, the compositional variation and the electrical resistivity of the hydrated cement paste. Two distinctive hydration stages can be differentiated from the BCSA cementitious materials. First stage is mainly controlled by hydration process of both the ye’elimite and the gypsum, and the second stage is mostly controlled by the formation of AFm and amorphous phases as a secondary hydration process. According to the classic equation depicted the hydration degree of cementitious materials, a specific mathematical equation combining not only traditional parameters but also the electrical resistivity is proposed for the BCSA.
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In dry-mortar-formulations calcium aluminate cement (CAC) is often used as a set accelerator for ordinary Portland cement (OPC). However, a critical amount of CAC is able to delay not only the ...silicate reaction but also the renewed C3A dissolution of an OPC. This delay can be counteracted by adding an appropriate amount of calcium sulfate (C$) to the mix OPC/CAC. The initial hydration period is dominated by fast ettringite formation from CA (CAC) and CaSO4 from OPC generating early strength. High aluminum and low calcium concentrations in the pore solution probably hinder C-S-H seeding and precipitation, thus preventing alite dissolution. Aluminum has to be initially removed by precipitating hydrate phases to change the pore solution chemistry. The start of the silicate reaction is then induced by increasing the calcium concentration in the pore solution.
Graphene oxide displays the great capability for cement composites and the complexity for the observation of nanomaterials in the scanning electron microscope (SEM) images. This paper proposes an ...intelligent model “improved Zhang network–based generalized particle swarm (IZN-GPS) algorithm” to analyze the microstructure characteristics of graphene oxide–reinforced cement composite. At first, the cement mortar was prepared by adding graphene oxide, ordinary Portland cement, water/cement ratio, and fine aggregates. The cement composite prepared is then investigated by the proposed algorithm using SEM images. These images are binarized using Otsu’s approach that displays the pores and solid materials in the cement composite as white and black colors, respectively. Finally, the proposed IZN-GPS algorithm accurately determines the microstructures of GO-reinforced OPC composite by extracting required information from the binary images. The training error generated in the improved Zhang network is minimized using generalized particle swarm (GPS) algorithm. As a result, the proposed IZN-GPS algorithm effectively analyzes the microstructures and indicates that the GO-reinforced OPC composite has fewer pore regions and exhibits high durability and strength properties. The performance of the proposed IZN-GPS algorithm is examined using different measures, namely durability, tensile strength, compressive strength, porosity, flexural strength, cost, and accuracy. The experimental results inherit that the proposed IZN-GPS algorithm using GO-reinforced OPC composite achieves greater accuracy, enhanced compressive strength, tensile strength, and durability with less porosity rate as compared to other techniques.
This paper intends to contribute to a better knowledge of the production and rehydration of thermoactivated recycled cement and its incorporation in cement-based materials. To this end, the influence ...of the treatment temperature on the properties of recycled cements and recycled cement pastes was assessed by means of a wide array of tests. Anhydrous recycled cement as well as the resulting pastes were characterized through density and particle size, water demand and setting time, thermogravimetry, X-ray diffraction, field emission gun scanning electron microscopy, isothermal calorimetry,
Si nuclear magnetic resonance spectroscopy, flowability, mechanical strength, mercury intrusion porosimetry and scanning electron microscopy. The treatment temperature had a significant influence on the dehydration and hydration of recycled cement, essentially resulting in the formation of C
S polymorphs of varying reactivity, which led to pastes of different fresh and hardened behaviors. The high water demand and the pre-hydration of recycled cement resulted in high setting times and low compressive strengths. The highest mechanical strength was obtained for a treatment temperature of 650 °C.
This study aims to compare the performance of sulphate resisting (SR) Portland cement mortar (SRm) and calcium aluminate cement mortars (CACm) in both natural sewer environment and sulphuric acid. ...Specimens were extracted after 12 and 24 months from field exposure, and were also removed from 1.5% sulphuric acid (H2SO4) after 6 months to investigate the deterioration caused by chemically induced corrosion. Visual, physical and extensive microstructural analyses were performed to evaluate the degradation of CACm and SRm matrix using techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX), X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. Surface pH was estimated after 12 and 24 months of field exposure to identify the initiation of biotic film development due to microbial induced corrosion (MIC). Material properties such as mass loss, compressive strength, linear expansion, and pH profile with respect to neutralization depth were also measured. The difference in mechanism of deterioration was also highlighted based on microstructural investigations between in field experimentation and acid exposure. The results showed that overall CACm performed significantly better than SRm in onsite sewer environment and sulphuric acid solution in terms of visual observations, loss in mass, compressive strength reduction, depth of neutralization, reduction in pH and penetration of sulphur. Crystallization of gypsum within the matrix of both mixes was the main factor behind the deterioration observed using XRD and FTIR from both in field and acid attack exposure, with higher deterioration within the matrix of SRm as compared to CACm. Moreover, sulphuric acid testing is suitable for screening the mixes rapidly against acidic environment, but due to the major differences observed in deterioration processes with natural field conditions this method is unsuitable for service life design of sewage structures.
The adoption of any binder system for structural concrete depends on the performance characteristics desired for addressing the long-term deformation and durability concerns. The major properties ...influencing the performance includes the shrinkage characteristics governing the long-term deformation, and durability characteristics related to various transport mechanisms, governing the performance in different service conditions. This paper describes the potential of Limestone Calcined Clay Cement (LC3) for use in structural concrete in comparison with Ordinary Portland Cement (OPC) and fly ash based blended cement (FA30). Three types of concrete mixtures were designed for the study, two based on achieving an equivalent strength grade (M30 and M50 concrete grade) with each binder, and the third with equal binder content and w/b ratio. Mechanical properties such as compressive strength and elastic modulus, and autogenous and drying shrinkage, along with various durability parameters of the different concretes were assessed. Oxygen permeability, rapid chloride penetration, chloride migration, resistivity development and water sorptivity were the various parameters considered for evaluation of durability performance. The results indicate the superiority of LC3 binder over other binders in producing durable concrete, especially in a chloride laden environment. The major reason for the better performance was attributed to the more compact and dense microstructure of the system with the LC3 binder against OPC and FA30. The drying shrinkage performance was seen to be similar for concrete with all three binders.
The cement industry is facing numerous challenges in the 21st century due to depleting natural fuel resources, shortage of raw materials, exponentially increasing cement demand and climate linked ...environmental concerns. Every tonne of ordinary Portland cement (OPC) produced releases an equivalent amount of carbon dioxide to the atmosphere. In this regard, cement manufactured from locally available minerals and industrial wastes that can be blended with OPC as substitute, or full replacement with novel clinkers to reduce the energy requirements is strongly desirable. Reduction in energy consumption and carbon emissions during cement manufacturing can be achieved by introducing alternative cements. The potential of alternative cements as a replacement of conventional OPC can only be fully realized through detailed investigation of binder properties with modern technologies. Seven prominent alternative cement types are considered in this study and their current position compared to OPC has been discussed. The study provides a comprehensive analysis of options for future cements, and an up-to-date summary of the different alternative fuels and binders that can be used in cement production to mitigate carbon dioxide emissions. In addition, the practicalities and benefits of producing the low-cost materials to meet the increasing cement demand are discussed.
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