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This paper presents selected findings from a recently completed research project, aimed at the investigation of CO 2 sequestration in cement-based materials during the early stages of hydration when the cement paste is being mixed. Portland cement pastes were carbonated during the mixing process, using both carbonated water and gaseous CO 2 , and their properties were compared to the control non-carbonated mix. All mixes were prepared in a purpose-designed chamber that permitted carbonated water and gaseous CO 2 to be mixed with the cementbased materials during the mixing process, without losses of CO 2 to the external environment. Temperature measurements taken of the samples during mixing were used to evaluate the influence of carbonation on the properties of fresh pastes and their early hydration. Changes in the composition of the hardened pastes, due to the above-mentioned processes, were studied using thermogravimetric (TG) analysis, X ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR). Scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDXS) were used to investigate physical (morphological) and chemical differences between non-carbonated and carbonated samples.It was found that, when compared to the non-carbonated mixes, the rate of the initial hydration of carbonated pastes increased, but the later hydration rate was decreased dramatically. TG, XRD, and FTIR spectroscopy revealed a substantial increase in the CaCO 3 content and decrease in the Ca(OH) 2 content in carbonated pastes. SEM showed substantial differences in the microstructure of the carbonated mixes when compared to the noncarbonated ones; needle-and lichen-like hydrates, with a high content of CO 2 , covered the surface of the fractured carbonated samples.

This paper summarises an investigation into the potential advantages to the precast concrete industry of using a new 'seeding' type of chemical admixture in Portland cement (PC) based concrete mixes. Results indicated that the addition of 2-4% nanocrystal seeding chemical (NCS) admixture by weight of PC can provide a doubling of early strength, particularly at 6 and 12 h. This strength gain could lead to the turnover of moulds in precast concrete plants being completed twice in 24 h, thus increasing production capacity. Isothermal conduction calorimetry, X-ray diffraction and thermogravimetric analysis techniques were used to investigate the reasons for the improvement in compressive strength development. Results indicated that the increase in early compressive strength is due to an acceleration of early hydration of PC in presence of the NCS. Indeed, after 6 h, the degree of hydration was more than 50% greater when NCS was used. This paper also highlights the possibility of the NCS chemical admixture being used in conjunction with supplementary cementitious materials (SCMs) in PC blended concrete mixes. 2% NCS was added to a blend containing 70% PC and 30% ground granulated blast furnace slag (GGBS). Results indicated that early strength values were greater compared to the blend without NCS and comparable to the 100% PC mix.

This paper reports the findings of research on the environmental performance of two case study houses, a retrofit and new build. The retrofit was completed to a PassivHaus standard whilst the new build was completed to current Irish building regulations. Environmental performance of the retrofit and new build was measured using life cycle assessments, examining the assembly, operational and end of life stage over life spans of 50 and 80 years.Using primary information, LCA software and LCA databases the environmental impacts of each stage were modelled. The operational stage of both case studies was found to be the source of the most significant environmental damage, followed by the assembly and the end of life stage respectively. The relative importance of the assembly and end of life stage decreased as the life span increased. It was found that the retrofit house studied outperformed the new build in the assembly and operational stage whilst the new build performed better in the end of life stage however this is highly sensitive, depending on the standards to which both are completed. Operational energy savings pre and post-retrofit were significant indicating the future potential for adoption of high quality retrofitting practices.