Daman K. Panesar

Life-cycle cost analysis of highway noise barriers designed with photocatalytic cement

This study examines the environmental and economic feasibility of concrete noise barriers containing photocatalytic cement using a life-cycle cost analysis (LCCA). Photocatalytic concrete contains titanium dioxide (TiO2) which allows for the oxidation of air pollutants to occur on the surface of the building material. Design variables studied include the cementing material type (general use (GU) cement, ground granulated blast furnace slag (GGBFS) used as cement replacement, and photocatalytic (PCAT) cement), and the thickness of a photocatalytic concrete cover. The LCCA accounts for the CO2 and NOx generated during manufacturing and the NOx (NO, NO2) oxidised during the life of barriers containing photocatalytic concrete. A key outcome from this study revealed that at a 40-year service life, assuming a 6 mg/h/m2 NOx degradation rate, a barrier designed with 100%GU cement and a 25 mm photocatalytic concrete cover has an annual cost that is 7%, 30%, and 36% greater than the 100%GU, 35% and 50%GGBFS barriers without a photocatalytic cover, respectively. Results of this analysis also indicated that the application of a 25 mm photocatalytic concrete cover to concrete containing 35 and 50%GGBFS is more economically feasible than 100%GU concrete, irrespective of the service life and pollution degradation rate.

Impact of the selection of functional unit on the life cycle assessment of green concrete

PurposeThe objectives of this study are to evaluate life cycle assessment (LCA) for concrete mix designs containing alternative cement replacement materials in comparison with conventional 100% general use cement concrete and to evaluate the interplay and sensitivity of LCA for four concrete mix designs and six functional units which range in degrees of complexity and variables.MethodsSix functional units with varying degrees of complexity are included in the analysis: (i) volume of concrete, (ii) volume and 28-day compressive strength, (iii) volume and 28-day rapid chloride permeability (RCP), (iv) volume and binder intensity, (v) volume and a combination of compressive strength and RCP and (vi) volume and a combination of binder intensity and RCP. Four reference flows are included in the analysis: three concrete mix designs containing slag, silica fume and limestone cement as cement replacement and one concrete mix design for conventional concrete.Results and discussionAll three alternative mix designs were evaluated to have lower environmental impacts compared with the base 100% general use cement and so are considered to be ‘green’ concrete. Similar LCA results were observed for FU1, FU2 and FU4, and relatively similar results were obtained for FU3, FU5 and FU6. LCA conducted with functional units which were a function of durability exhibited markedly different (lower) LCA compared with the functional units that did not capture long-term durability.ConclusionsOutcomes of this study portray the interplay between concrete mix design materials, choice of functional unit and environmental impact based on LCA. The results emphasize (i) the non-linearity between material properties and environmental impact and (ii) the importance of conducting an LCA with a selected functional unit that captures the concrete’s functional performance metrics specific to its application and expected exposure conditions. Based on this study, it is recommended that a complete LCA for a given concrete mix design should entail examination of multiple functional units in order to identify the range of environmental impacts or the optimal environmental impacts.

Criteria for the evaluation of life cycle assessment software packages and life cycle inventory data with application to concrete

PurposeLife cycle assessment (LCA) software packages have proliferated and evolved as LCA has developed and grown. There are now a multitude of LCA software packages that must be critically evaluated by users. Prior to conducting a comparative LCA study on different concrete materials, it is necessary to examine a variety of software packages for this specific purpose. The paper evaluates five LCA tools in the context of the LCA of seven concrete mix designs (conventional concrete, concrete with fly ash, slag, silica fume or limestone as cement replacement, recycled aggregate concrete, and photocatalytic concrete).MethodsThree key evaluation criteria required to assess the quality of analysis are adequate flexibility, sophistication and complexity of analysis, and usefulness of outputs. The quality of life cycle inventory (LCI) data included in each software package is also assessed for its reliability, completeness, and correlation to the scope of LCA of concrete products in Canada. A questionnaire is developed for evaluating LCA software packages and is applied to five LCA tools.Results and discussionThe result is the selection of a software package for the specific context of LCA of concrete materials in Canada, which will be used to complete a full LCA study. The software package with the highest score is software package C (SP-C), with 44 out of a possible 48 points. Its main advantage is that it allows for the user to have a high level of control over the system being modeled and the calculation methods used.ConclusionsThis comparative study highlights the importance of selecting a software package that is appropriate for a specific research project. The ability to accurately model the chosen functional unit and system boundary is an important selection criterion. This study demonstrates a method to enable a critical and rigorous comparison without excessive and redundant duplication of efforts.

The influence of design variables and environmental factors on life-cycle cost assessment of concrete culverts

The objective of this article is to evaluate the influence of material, structural design variables and exposure conditions on the service life and cost effectiveness of precast concrete culverts in Canada. This investigation will assist practicing engineers to account for long-term performance and integrate life cycle analysis into design and construction decisions. The design variables considered in this study include the percentage of ground granulated blast furnace slag (GGBFS) as cement replacement, reinforcing steel cover depth and culvert size. This study proposes the usage of a life-cycle cost assessment approach to compare different culvert designs on an economic basis which accounts for the design variables and the impact of CO2 production and uptake over the life of a culvert from cradle to grave. Analysis of each culvert scenario includes the cost of the initial production of CO2 during the manufacturing process as well as the cost savings that were incurred due to the uptake of CO2 through carbonation processes. Overall, the present cost of the culverts is controlled by the GGBFS content and the reinforcing steel cover depth while carbonation processes have a relatively small economic impact.

Effect of Multiaxial Stresses on Alkali-Silica Reaction Damage of Concrete

INTRODUCTION Alkali-silica reaction (ASR) is a serious deterioration problem in many concrete structures around the world.1 The reaction causes expansion, cracking, and degradation of mechanical properties of concrete. Although generally it is now possible to construct new structures safe against ASR, the greatest challenge remains to ensure the performance of existing ASR-affected structures by assessing ASR damage. Damage assessment of ASR-affected concrete usually relies on measuring expansion, monitoring cracking, and testing mechanical properties. Measurements on unrestrained specimens have established expansion as a characteristic of ASR. However, concrete in structures is often subjected to stresses in one or multiple directions and, hence, expansion measured on unrestrained laboratory specimens does not appropriately

The effect of sodium hydroxide surface treatment on the tensile strength and elastic modulus of cellulose nanofiber

The use of cellulose nanofibers in the reinforcement of polymers has applications in bio-based building materials. However, one problem observed when using cellulose nanofibers within composites is the difficulty of ensuring their adequate dispersion. The phenomenon of agglomeration is attributed to the high density of polarized hydroxyl groups at the surface of cellulose nanofibers. Initial observations indicate that cellulose nanofiber agglomeration, in a cement matrix at volume fractions larger than 0.1%, are theorized to have contributed to the brittle failure mode of the paste. In order to expand the use of cellulose nanofibers in bio-based building materials, it is necessary to reduce their agglomeration and improve their dispersion within a polymer through surface modifications in an effort to improve their reinforcing capability in composite materials. As such, a mild alkali treatment with sodium hydroxide (NaOH), also known as mercerization, was chosen for use in this study due to its longstanding establishment as a common, low cost, and simple process. Alkali treatment was found to improve the values of tensile strength and modulus, compared to the untreated strips, by 20% and 24%, respectively. These results could be attributed to the rearrangement of fibrils along the direction of tensile deformation, as a result of the dissolution of lignin and hemicelluloses fractions.