Multifunctional Lightweight Aggregate Containing Phase Change Material and Water for Damage Mitigation of Concrete

This paper presents an innovative concept of multifunctional lightweight aggregate, which is produced by loading phase change material (PCM) into the interior of lightweight sand (LWS) and sealing the surface pores using water. The PCM loaded in the LWS functionalizes it as a temperature management agent in concrete, and the water in surface pores enables internal curing. It has been found that the particle shape and pore structure of crushed expanded shale LWS makes it an ideal carrier for PCM, loading sufficient PCM and maintaining better (compared to natural sand) mechanical interlocking. When coupled with the internal curing effect, the LWS yields an interpenetrated interfacial transition zone with the cement paste, leading to a compressive strength comparable to natural sand mortar. The hydration products penetrated into the surface pores also helps stabilizing PCM in the LWS. However, any PCM residuum non-stabilized in LWS tends to compromise the strength. Under an optimized scenario, the LWS-PCM composite aggregate is produced by grading, PCM impregnation, rinsing, and water saturation. A mortar proportioned with this aggregate yields comparable 28-day strength to the reference mortar and a 63% lower autogenous shrinkage (because of internal curing). Furthermore, it shows a 7 ⁰C lower semi-adiabatic temperature rise, delayed appearance of peak temperature and gentled cooling curve. These results indicate that the functional aggregate can effectively mitigate the risk of thermal cracking in early-age mass concrete. In addition, PCM remained in aged concrete has a potential to improve its adaptivity to temperature fluctuations in the service environment

Development And Characterization Of Coal-Based Thermoplastic Composite Material For Sustainable Construction

The exploitation of coal and the disposal of waste plastic present significant environmental and economic challenges that require sustainable and profitable solutions. In response, we propose a renewable construction composite material of coal-based thermoplastic composite (CTC) that can be made from low-grade coal and plastic waste. We developed and tested the hot-press fabrication method for this CTC, using coal with a maximum particle size of 4.75 mm and recycled high-density polyethylene (HDPE). The effects of the coal fraction (50–80 wt.%) on compressive properties, thermal properties, microstructure, and ecological and economic efficiencies of the CTC were investigated. Test results revealed that the compressive strength and modulus decrease as the coal fraction increases. However, the thermal properties, including thermal conductivity and specific heat, increase with higher coal contents. Compared to concrete, the CTC has about half the thermal conductivity and twice the specific heat, making it a more energy-efficient construction material. Microstructure testing helped to reveal the mechanisms behind the above behaviors of CTC from the observation of binder volume, bonding quality between coal and HDPE, and porosity variation. The life cycle analysis indicated that the CTC production reduced embodied energy, carbon footprint, and cost by up to 84%, 73%, and 14%, respectively. Therefore, we recommend the CTC with 50–70% coal fraction as an innovative construction material with satisfied mechanical and thermal properties, better cost efficiency, and a reduced ecological impact

In Situ Monitoring Of The Hydration Of Calcium Silicate Minerals In Cement With A Remote Fiber-optic Raman Probe

This study utilized a novel in situ fiber-optic Raman probe to continuously monitor the hydration progress of tricalcium silicate (C3S) and dicalcium silicate (C2S) without the need for sampling, from early hydration stage to later stages, and from fresh to hardened states of paste samples. By virtue of the remarkable ability of this technique in characterizing either dry or wet and crystalline or amorphous samples, the hydration processes of C3S and C2S pastes with different water-to-solid (w/s) ratios could be monitored from the start of the hydration reaction. The main hydration products, calcium silicate hydrate (C–S–H) and portlandite/calcium hydroxide (CH), have been successfully identified and continuously monitored for variations in their respective amounts in situ. The effect of w/s ratio on the hydration processes of C3S and C2S pastes was also considered. Meanwhile, the x-ray diffraction (XRD) and thermogravimetric analysis (TGA) results showed a great correlation with the in situ Raman test results about hydration products, which demonstrated the reliability of this technology. Moreover, the signal-to-noise ratio (SNR) of this Raman probe is significantly superior to existing technologies for in situ fiber-optic Raman spectroscopy. This remote fiber-optic Raman probe enables the use of Raman spectroscopy in future construction projects for on-site monitoring and evaluation of health conditions and performance of concrete structures

Investigation of Corrosion Mechanism of Ribbed Mild Steel Bars Coated with Magnesium Potassium Phosphate Cement Paste

This Study Investigated the Anti-Corrosion Performance of Magnesium Potassium Phosphate Cement (MKPC) Paste Applied to the Surface of Ribbed Mild Steel Bars – Which Was Exposed to Simulated Accelerated Corrosive Environment. Four Electrochemical Approaches Were Used Including Open-Circuit Potential (OCP), Electrochemical Impedance Spectroscope (EIS), Polarization Resistance (PR) and Potentiodynamic Polarization (PDP) over a Period of 5376 H (224 Days). Moreover, Visual Inspection, Optical Microscope, and Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS) Were Used to Assess the Extent of Corrosion on the Samples. to Understand the Mechanism of Corrosion Protection of the Coating System, X-Ray Photoelectron Spectroscopy (XPS) Was Employed to Characterize the Chemical Groups on the Surface of Mild Steel, and the Chemical Changes in the Coating Layer Were Characterized using Thermogravimetric/differential Thermal Analysis (TG/DTA) and X-Ray Diffraction (XRD). the MKPC Paste Coated Bars Were Compared with Not Only Uncoated Bars, But Also Bars Coated with Ordinary Portland Cement (OPC) that is Known to Passivate Steel Due to its High Alkalinity. Results Indicated that MKPC Paste Coating Layer Could Effectively Protect the Ribbed Mild Steel Bars, and its Protectiveness Significantly Surpassed that of OPC. Both the De-Passivation Effects of Chloride Ions and Carbonation of the OPC Resulted in Relatively Severe Corrosion of the OPC Coated Bars during the Long Exposure Duration; While the Anti-Corrosion Merit of the MKPC Paste Coating Layer Could Be Attribute to a Double-Protection System– the Dense Microstructure of MKPC and the Formation of an Iron (III) Phosphate Passivation Layer between the Substrate Steel and the MKPC Paste Coating Layer

Robust joint sparsity model for hyperspectral image classification

Sparsity-based classification methods have been widely used in hyperspectral image (HSI) classification. These methods typically assumed Gaussian noise, neglecting the fact that HSIs are often corrupted by different types of noise in practice. In this paper, we develop a robust super-pixel level joint sparse representation classification model (RSJSRC) to address the mixed noise problem in sparsity-based HSI classification. Our method takes into account both Gaussian and sparse noise. Experimental results on simulated and real data demonstrate the efficiency of the proposed method and clear benefits from the introduced mixed-noise model

Densifying Hydration Products of Alite by a Bio-Inspired Admixture

A bio-inspired, plant-derived polyphenol, tannic acid (TA) was identified as a renewable admixture to improve the compressive strength of concretes. Aiming to understand the underlying mechanism responsible for this strength improvement, this study examines how TA mediates the hydration of tricalcium silicate (alite). Experimental study shows that TA can form complex with calcium ions through chelating, retarding the hydration of the alite and changing of the hydration products. Particularly, X-ray diffraction analysis shows that TA makes calcium hydroxide preferentially grow on the [0 0 1] face. Fourier-transform infrared spectroscopy and 29Si MAS NMR results reveal that the mean chain length of calcium silicate hydrate (C[sbnd]S[sbnd]H) is reduced by TA. More importantly, mercury intrusion porosimetry testing reveals that pores with size near 30 nm was almost eliminated by adding TA, leading to higher elastic modulus of the produced C[sbnd]S[sbnd]H and higher compressive strength of the produced concrete

Weighted sparse graph based dimensionality reduction for hyperspectral images

Dimensionality reduction (DR) is an important and helpful preprocessing step for hyperspectral image (HSI) classification. Recently, sparse graph embedding (SGE) has been widely used in the DR of HSIs. In this letter, we propose a weighted sparse graph based DR (WSGDR) method for HSIs. Instead of only exploring the locality structure (as in neighborhood preserving embedding) or the linearity structure (as in SGE) of the HSI data, the proposed method couples the locality and linearity properties of HSI data together in a unified framework for the DR of HSIs. The proposed method was tested on two widely used HSI data sets, and the results suggest that the locality and linearity are complementary properties for HSIs. In addition, the experimental results also confirm the superiority of the proposed WSGDR method over the other state-of-the-art DR methods

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