Influence of Slag Composition and Temperature on the Hydration and Performance of Slag Blends in Chloride Environments

The use of GGBS as supplement for cements has been shown to improve the long-term strength and durability properties of concrete. In practice, while the chemical composition of GGBS from a single plant may be constant, due to the varying sources from which GGBS is obtained the chemical composition from plant to plant may vary. The wide variability in the use of GGBS as a SCM in different climates, coupled with differences in chemical composition, is bound to have impact on the performance of slag blends. This study investigated the combined influence of difference in slag composition and temperature on the performance of slag blends. Performance was evaluated in terms of strength and transport properties. Paste samples were characterised by calorimetry, TGA, XRD and SEM to follow hydration and microstructural development. Mortar samples were used to follow strength development and transport properties. All tests were carried out at temperatures of 20 and 38°C. Curing at 38°C accelerated the early hydration, but not the later hydration. This led to higher early strengths and lower later strengths, and was attributed to the coarsening of the pore structure caused by the high temperature curing. Except at the early ages at 20°C, both slag blends showed better strength performance than the reference cement. The slag blends also showed better transport properties than the reference cement, especially at 38°C, and this was attributed to their finer pore structure and higher chloride binding capacity. Of the two slags studied, the more reactive slag (slag 1) had better performance, especially at 38°C. Performance of the slag blends at 20°C was influenced mainly by the length of curing, and by the difference in chemical composition at 38°C

The effect of slag composition and curing duration on the chloride ingress resistance of slag-blended cements

This paper reports the influence of varying curing durations on the chloride ingress resistance of slag blends. Samples were prepared by combining two slags (S1 and S2) with CEM I 52·5R cement at 30% by weight of slag. Mortar samples were cured for either 7 or 28 d, before being exposed to a 3% sodium chloride solution. Samples were subjected to two chloride exposure conditions (either complete submersion or a cyclic 6 h wetting and drying cycle). Depths of free chloride penetration as well as total and water-soluble chloride contents were measured for the exposed samples. Samples cured for 28 d before exposure showed far better resistance to chloride ingress than those cured for 7 d. The cement–slag blend with S1, having an alumina content of 12·23%, performed better than the blend with S2 (alumina content of 7·77%), especially for samples cured for 7 d. This was attributed to the higher basicity of S1. However, when the samples were cured for 28 d, the difference between the performances of the slag blends became minimal. Despite this, the overall performance of the slag blends, which was compared against a CEM I 42·5R-type cement, was found to be better at both curing durations

Performance Evaluation of Rice Husk Ash as Partial Replacement of Cement in Concrete in a Marine Environment at Escravos River, Niger Delta Area, Nigeria

Cement has proven to cause environmental problems during its production and to be a relatively high-cost material in concrete production. Environmentally friendly, alternative binders like Rice Husk Ash (RHA) have recently been brought to bear. Therefore, the objective of this paper is to evaluate the performance of RHA (under controlled temperature and burning time) as a partial (10% and 20%) replacement of cement in concrete in a marine environment at Escravos River, Niger Delta Area, Nigeria. Concrete samples prepared with the 10% and 20% RHA in the laboratory were exposed to brackish water samples from the Escravos River, at 3 days, 7 days, 28 days and 90 days and the results compared with that of PLC concrete cast. Data obtained show that the workability of fresh concrete reduced with increase in RHA and further reduced, mixing with salt water. RHA contributed positively to the setting time of the concrete as it increased the initial setting time and reduced final setting time. 10%RHA concrete performed best under all conditions, with about 10% increase in strength. Further increase led to a slight decline in strength. As the amount of RHA increased, the ability of the concrete to resist chloride penetration, increased, with lesser average penetration depth. 10%RHA concrete showed the strongest rebar-concrete bond. 10% RHA is optimum for partial replacement of cement in concrete in marine environment, as it enhances the performance of the concrete

Compressive Strength and Resistance to Sodium Sulphate Attack of Concrete Incorporated with Fine Aggregate Recycled Ceramic Tiles

In this experimental study, compressive strength and resistance to sodium sulphate attack of concrete incorporating recycled ceramic tiles (RCT) as fine aggregate were investigated. RCT was used as partial replacement for river sand at four levels (0%, 33%, 66%, 100%). Samples for sulphate resistance tests were immersed in 5% Na2SO4 solution for 180 days after they had been cured under water for 28 days, and were monitored for change in physical appearance, mass change and loss of compressive strength. From experimental results, RCT was found to be capable of producing light weight concrete compared to river sand. The results showed increase in compressive strength as the level of RCT content increased. On resistance to sulphate attack, sodium sulphate seems not to attack C-S-H bond which is produced in excess in RCT concrete, rather it attacks calcium hydroxide and calcium aluminate which are produced in equal amounts for both RCT and control samples. Hence, RCT might not play much direct role in concrete’s resistance to strength loss due to sulphate attack. However, the residual compressive strength of the RCT samples after the attack was seen to be much higher than that of the control samples because of their initial higher strength before the attack. This shows that RCT can improve the properties of concrete when incorporated as fine aggregates

Effect of Curing Age on the Prospect of Used Plastics to Enhance Engineering Properties of Road Pavements within a Development and Property Agency Estate in Benin City, Edo State, Nigeria

This study investigated the effect of curing age on the possibility of using plastic powder to enhance the engineering properties of subgrade for road pavements. The soil samples utilized for the study were collected from four distinct locations within the Edo Development and Property Agency estate in Benin City, Edo State, Nigeria using appropriate standard methods. They were stored in airtight polythene bags and taken to the University of Benin Geotechnical Laboratory for testing. Polyethylene terephthalate (PET) plastics sourced from recycled soft drink and bottled water containers were pulverized and added to the soil in various proportions of 2%, 4%, 6%, 8% and 10% by weight of the soil. The resulting mix was subjected to various tests such as Atterberg limits, compaction and California Bearing Ratio (CBR). The results showed that the addition of the PET plastic powder led to substantial transformation in the soil’s properties. There was a reduction in the liquid limit, plastic limit and plasticity index, as the proportion of the plastic powder increased. The maximum dry density (MDD) and the optimum moisture content (OMC) was also seen to increase and decrease correspondingly as the proportion of the plastic powder was increased in the soil. The results also showed that as proportion of the plastic powder in the soil was increased, the CBR of the soil also increased. This increase in the soil strength was also observed as the curing age of the CBR samples increased from 0 to 14 days. This shows that a combination of extended curing periods and a larger proportion of plastic powder can significantly improve the load-bearing capacity and saturation resistance of the soil. This study underscores the considerable potential of plastic powder stabilization in elevating the engineering properties of subgrade materials, thereby conferring notable benefits to the domain of road pavement construction

Performance of plain and slag-blended cements and mortars exposed to combined chloride-sulphate solution

The durability of reinforced concrete structures exposed to aggressive environments remains a challenge to both researchers and the construction industry. This study investigates the hydration, mechanical properties and durability characteristics of ground granulated blast-furnace slag (GGBS) - blended cements and mortars exposed to a combined sodium chloride - sulphate environment, at temperatures of 20°C and 38°C. The conditions were chosen so as to assess the performance of slag blends under typical temperate and warm tropical marine climatic conditions. Slags, having CaO/SiO2 ratios of 1.05 and 0.94, were blended with CEM I 52.5R at 30% replacement level to study the influence of slag composition and temperature. Parallel control tests were carried out with CEM I 42.5R. Pastes and mortar samples were cast using 0.5 water to binder ratio, pre-cured for 7 days in water before exposure. Flexural strengths were determined once the samples were 7, 28 or 90 days old. Hydration was followed using x-ray diffraction (XRD), thermal analysis, and calorimetry. Also, sorptivity, gas permeability and chloride diffusion tests were carried out on mortar samples to measure transport and durability characteristics. The results show improved mechanical and transport properties for slag blended cements exposed to environments rich in sodium chloride and sulphate

Influence of slag composition and curing duration on the performance of slag blends in chloride environments

This study investigated the influence of chemical composition of Ground Granulated Blast Furnace Slag (GGBS) and curing duration on the performance of slag-cement blends; specifically strength and transport properties. Two slags (1 and 2) with Ca/Si ratios of 1.05 and 0.94 respectively, were used to partially replace 30% of a CEM I 52.5R cement. Various tests, including compressive strength, isothermal calorimetry, water absorption, sorptivity, and chloride ingress were conducted on mortar specimens to measure the performance of the slag blends against a CEM I 42.5R cement. The mortar specimens were pre-cured for 7 and 28 days before exposure to a 3% sodium chloride solution. Two different exposure conditions were studied (one in which the samples were submerged completely in the salt solution, and the other in which the samples were subjected to a 6 hr wetting and drying cycle). The results obtained showed similar performance for both slags at longer curing durations; with the more basic slag 1 exhibiting better transport properties than slag 2 for both exposure conditions at shorter curing durations. This suggests that curing duration as well as variation in chemical composition of slags affects the performance of slag blends in chloride environments

Improvement of deltaic lateritic soil using river sand and cement for use as pavement construction material

This study examined the effect of mechanical and chemical improvement on deltaic lateritic soils in Warri East in Delta State, Nigeria. Mechanical stabilization was carried out by adding river sand to the natural soil in various proportions, while chemical stabilization was carried out using cement and a mixture of cement and sand. Compaction and CBR tests were conducted on the natural soil before and after stabilization. From the results obtained, it was seen that the mechanical stabilization method improved the strength properties of the soil making it suitable for use as subbase materials, though not as much as the chemical stabilization method or the mixed method of stabilization. It was concluded that using a combination of cement and sand as a stabilizing agent for deltaic lateritic soils can lead to significant reduction in the amount of cement required for soil stabilization thus saving costs

Chloride binding and diffusion in slag blends: Influence of slag composition and temperature

This study has investigated the impact of a change in GGBS chemical composition on the chloride ingress resistance of slag blended cements under different temperature regimes. Two slags, having alumina contents of 12.23 and 7.77% respectively, were combined with a CEM I 52.5 R at 30 wt% replacement. Chloride binding and diffusion tests were conducted on paste and mortar samples respectively. All tests were carried out at temperatures of 20 °C and 38 °C. The higher temperature resulted in an increase in chloride binding; attributed to greater degrees of slag hydration. Despite this, chloride ingress was greater at 38 °C; attributed to changes in the pore structure and the chloride binding capacities of the slag blends. The more reactive, aluminium-rich slag performed better in terms of chloride binding and resistance to chloride penetration, especially at the high temperature and this was attributed to its higher alumina content and greater degree of reaction at 38 °