Chloride-laden environments pose serious durability concerns in cement based materials. This paper presents the findings of chloride ingress in chemically activated calcined Clay-Ordinary Portland Cement blended mortars. Results are also presented for compressive strength development and porosity tests. Sampled clays were incinerated at a temperature of 800 ∘ C for 4 hours. The resultant calcined clay was blended with Ordinary Portland Cement (OPC) at replacement level of 35% by mass of OPC to make test cement labeled PCC35. Mortar prisms measuring 40 mm × 40 mm × 160 mm were cast using PCC35 with 0.5 M Na 2 SO 4 solution as a chemical activator instead of water. Compressive strength was determined at 28th day of curing. As a control, OPC, Portland Pozzolana Cement (PPC), and PCC35 were similarly investigated without use of activator. After the 28th day of curing, mortar specimens were subjected to accelerated chloride ingress, porosity, compressive strength tests, and chloride profiling. Subsequently, apparent diffusion coefficients ( app ) were estimated from solutions to Fick's second law of diffusion. Compressive strength increased after exposure to the chloride rich media in all cement categories. Chemically activated PCC35 exhibited higher compressive strength compared to nonactivated PCC35. However, chemically activated PCC35 had the least gain in compressive strength, lower porosity, and lower chloride ingress in terms of app , compared to OPC, PPC, and nonactivated PCC35.

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Blended cements are preferred to Ordinary Portland Cement (OPC) in construction industry due to costs and technological and environmental benefits associated with them. Prevalence of significant quantities of carbon dioxide (CO2) in the atmosphere due to increased industrial emission is deleterious to hydrated cement materials due to carbonation. Recent research has shown that blended cements are more susceptible to degradation due to carbonation than OPC. The ingress of CO2 within the porous mortar matrix is a diffusion controlled process. Subsequent chemical reaction between CO2 and cement hydration products (mostly calcium hydroxide [CH] and calcium silicate hydrate [CSH]) results in degradation of cement based materials. CH offers the buffering capacity against carbonation in hydrated cements. Partial substitution of OPC with pozzolanic materials however decreases the amount of CH in hydrated blended cements. Therefore, low amounts of CH in hydrated blended cements make them more susceptible to degradation as a result of carbonation compared to OPC. The magnitude of carbonation affects the service life of cement based structures significantly. It is therefore apparent that sufficient attention is given to carbonation process in order to ensure resilient cementitious structures. In this paper, an indepth review of the recent advances on carbonation process, factors affecting carbonation resistance, and the effects of carbonation on hardened cement materials have been discussed. In conclusion, carbonation process is influenced by internal and external factors, and it has also been found to have both beneficial and deleterious effects on hardened cement matrix.

This paper presents findings of an experimental investigation on sodium sulphate (Na2SO4) activated calcined clay – Portland cement blends in sulphuric acid media. Calcined clays were blended with Ordinary Portland Cement (OPC) at replacement levels of 40% 45% and 50 % by mass of OPC to make blended cement labelled PCC40, PCC45 and PCC50 respectively. Initially, pozzolanicity and setting time tests were conducted. Mortar prisms measuring 40 mm × 40 mm × 160 mm were cast using 0.5M Na2SO4 solution and their compressive strengths determined on the 2nd, 7th, 28th and 90 th day of curing. The 28th day cured mortar prisms were subjected to porosity test. Moreover, 5 × 5 × 5 cm mortar cubes were also prepared and their weight and strength loss was taken as a measure of their acid resistivity after an immersion time of 7, 14, 28, 56, 84 and 120 days in 3 % of sulphuric acid at 23 ± 1 °C. OPC, commercial Portland Pozzolana Cement (PPC) and PCC40, PCC45 and PCC50 cement were cast using water and similarly investigated for comparison purposes. The results obtained showed that chemically activated cements exhibited higher pozzolanic activity, lower porosity, shorter setting times and higher resistance to acid attack compared to non-activated cements. However, OPC was found to be non-pozzolanic.

Cement structures are major capital investments globally. However, exposure of cement-based materials to aggressive media such as chloride- and sulphate-laden environments such as coastal areas affects their performance. Ordinary Portland cement (OPC) is the main cement used in buildings and civil structures such as dams and bridges. This paper reports the findings of an experimental investigation on the effect of ingress of Cl− and SO42− on compressive strength development and the ions’ diffusivity in selected OPC brands in Kenya. The aggressive media used included seawater (SW) and wastewater from leather industry (WLI). Three brands of commonly used cements of OPC in Kenya were used. Mortar prisms were prepared from each brand of cement at different water-to-cement ratios (w/c) of 0.5, 0.6, 0.65, and 0.7 and allowed to cure for 28 days in a highly humid environment. The aggressive ions’ ingress in the mortar prisms was accelerated using a potential difference of 12 V ± 0.1 V. Analysis of diffusivity and diffusion coefficient of Cl− and SO42− was finally done. Compressive strength analysis was done before (at the 2nd, 7th, 14th, and 28th day) and after exposure to the aggressive ions. The results showed that the diffusivity of chlorides was more pronounced than that of sulphates. Diffusivity was observed to be higher at higher w/c ratios for all cement categories. It was observed that compressive strength increased with curing age, with the highest observed at 28 days. Cement A was generally found to have the highest compressive strength for all w/c ratios. The compressive strength was observed to increase after the mortar prisms were exposed to SW as opposed to the ones exposed to WLI. Generally, it was also observed that the strength gain increased with increase in w/c. The loss in strength was also observed to increase with increase in w/c.

This paper reports leach and/or intake of SO42−, Cl−, Ca2+, Na+, and K+ from and/or into cement mortar cubes made from a novel cementious material in naturally encountered environmental simulated media. The paper also reports changes in pH of the media over time of exposure to the cement mortar cubes. The compressive strength changes of the test cement in simulated media are also reported. The novel cement, labelled PCDC, made from intermixing ordinary Portland cement (OPC) with waste materials which included rice husks, waste bricks, acetylene lime sludge, and spent bleaching earth was previously tested and found to meet the Kenyan Standard requirements for Portland pozzolana cement (PPC). 100 mm mortar cubes were prepared, and their compressive strengths were determined after exposure to the sea water. The media included sea water, distilled water, and solutions of sulphates and chlorides separately for a period of six months. The tests were carried alongside commercial PPC and OPC. The results showed that the PCDC exhibited comparable selected ions intake and/or leach to PPC in sea water, sulphate solutions, and distilled water. In chloride solutions, the cement exhibited the highest leach in the selected ions except K+ and Na+ ions. The results further showed that PCDC exhibited lower pH in all the media compared to OPC and PPC. The tests showed that the novel cement can be used for general construction work in the tested media in a similar manner to PPC.

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