Ordinary Portland Cement Samples Research Articles

Acoustic emission detection of microcrack formation and development in cementitious wasteforms with immobilised Al

An acoustic emission (AE) technique was applied for early detection, characterisation and time progress description of cracking phenomenon caused by the corrosion of Al encapsulated in cement matrix. The study was conducted on an ordinary Portland cement (OPC) system encapsulating high purity Al bar. Acoustic signals were generated and released during immersing of the sample in deionised water. A computer controlled PCI-2 based AE system processed the signals detected by piezoelectric transducers. A subsequent comparative study of the AE data collected with those obtained from a reference OPC sample has been applied. Recorded AE activity confirmed that the process of initiation and development of Al corrosion causes significant mechanical stresses within the cement matrix. Our analysis demonstrated possibility to differentiate AE signals based on their characteristics, and potentially correlate detected AE with the fracture processes in the cement system encapsulating Al.

Sulfate attack on alkali-activated slag concrete

This paper presents an investigation into durability of alkali-activated slag (AAS) concrete in sulfate environment. Two tests were used to determine resistance of AAS concrete to sulfate attack. These tests involved immersion in 5% magnesium sulfate and 5% sodium sulfate solutions. The main parameters studied were evolution of compressive strength, products of degradation, and microstructural changes. After 12 months of exposure to the sodium sulfate solution, the strength decrease was up to 17% for AAS concrete and up to 25% for ordinary Portland cement (OPC) concrete. After the same period of exposure to the magnesium sulfate solution, the compressive strength decrease was more substantial, up to 37% for OPC and 23% for AAS. The main products of degradation were ettringite and gypsum in the case of Portland cement and gypsum in AAS. OPC samples had significant expansion, cracking, and loss of concrete, while AAS samples were not expanded but cracked in the test. During experiments with the sodium sulfate solution, some increase in strength of AAS concrete was recorded, likely due to continuing hydration.

The hardening of Portland cement observed by1H spin-lattice relaxation and single-point imaging

The nature of hydration in ordinary Portland cement samples from different Polish factories was investigated by the proton spin-lattice relaxation timeT1 and single-point imaging (SPI). The time dependence of the spin-lattice relaxation timeT1 shows the usual behavior:T1 is constant at the beginning of hydration (the dormant period), then, during the setting process, decreases to the constant value in the hardening period of hydration. However, there are some anomalies inT1 connected with the different amount of the mineral components in the cement sample. The unusual behavior of the stretched parameterα, after about 20 h of hydration, is observed and connected with the microcracking of the cement matrix. The 1-D and 2-D SPI images of the cement paste taken at various times of hydration show the distribution of the water throughout the sample and clearly demonstrate the usefulness of SPI in the study of the internal structure of the porous system.

Experimental measurements of chloride ion diffusion rates using a two-compartment diffusion cell: Effects of material and test variables

Chloride ion diffusion rates in cementitious paste have been determined using a modification to the “standard” two-compartment diffusion cell. Ordinary Portland cement samples of varying water/cement ratios were investigated together with similar materials to which varying amounts of pyrolysed scrap automotive polymer (Sheet Moulding Compound — SMC) had been added. The effects of changes in the experimental conditions (sample thickness, chloride ion concentration in first compartment) were also investigated. The chloride ion diffusivity was reduced by either reducing the water/cement ratio or by the incorporation of pyrolysed SMC into the mix. There was a small decrease in effective chloride ion diffusivity with increase in sample thickness. The concentration of chloride ion in Cell 1 had no significant effect on the measured diffusivity. However, by increasing the concentration, the time required to make the diffusivity measurements can be significantly reduced.