197 research outputs found
Service life and life-cycle assessment of reinforced concrete with fly ash and limestone calcined clay cement
No full textEnvironmental impact due to the emission of carbon dioxide during concrete production can be taken care by reducing the clinker content in the cement. The clinker content can be reduced by replacing it with fly ash and limestone calcined clay. Such systems can have a potential to exhibit enhanced durability/service life when exposed to chloride and carbon dioxide. However, estimating probabilistic service life of concretes with such alternative binder systems is difficult due to the lack of quantitative estimates of the input parameters such as chloride diffusion coefficient (DCl), ageing coefficient (m), carbonation coefficient (KCO2), and chloride threshold (Clth). This paper presents the experimentally observed estimates of these parameters for the following systems: (I) 100% OPC, (II) 70% OPC + 30% fly ash, and (iii) limestone calcined clay cement (LC3)-known as OPC, PFA, and LC3 concretes, respectively, herein. A total of three concrete mixes were designed. Also, based on these input parameters, the probabilistic service life estimates of a bridge pier and a girder made of these three concretes and exposed to chlorides and carbon dioxide are presented. For chloride ingress study, Fick's 2nd Law of diffusion and Clth have been used. For carbonation study, a recently developed model for estimating carbonation depth (using mixture proportion) have been used. Then, the life-cycle assessment (LCA) of these three concrete systems in terms of the CO2 emissions per unit of concrete per year of estimated service life is presented-for both chloride and carbonation induced corrosion. In chloride laden environments, the service life of the bridge pier and girder systems could be enhanced by about 10 times by using fly ash or LC3 concretes-for similar strength grade concretes. Also, the average annual CO2 emissions (during the expected service life) of PFA and LC3 concretes could be about 3 and 7 times, respectively, lower than that of OPC concretes of similar strength grade. In case of carbonation-induced corrosion, the limited experimental data indicate that the PFA and LC3 concretes could exhibit a lower service life and higher average annual CO2 emissions (during the expected service life) than OPC concretes.</p
Service life and life-cycle assessment of reinforced concrete with fly ash and limestone calcined clay cement
No full textEnvironmental impact due to the emission of carbon dioxide during concrete production can be taken care by reducing the clinker content in the cement. The clinker content can be reduced by replacing it with fly ash and limestone calcined clay. Such systems can have a potential to exhibit enhanced durability/service life when exposed to chloride and carbon dioxide. However, estimating probabilistic service life of concretes with such alternative binder systems is difficult due to the lack of quantitative estimates of the input parameters such as chloride diffusion coefficient (DCl), ageing coefficient (m), carbonation coefficient (KCO2), and chloride threshold (Clth). This paper presents the experimentally observed estimates of these parameters for the following systems: (I) 100% OPC, (II) 70% OPC + 30% fly ash, and (iii) limestone calcined clay cement (LC3)-known as OPC, PFA, and LC3 concretes, respectively, herein. A total of three concrete mixes were designed. Also, based on these input parameters, the probabilistic service life estimates of a bridge pier and a girder made of these three concretes and exposed to chlorides and carbon dioxide are presented. For chloride ingress study, Fick's 2nd Law of diffusion and Clth have been used. For carbonation study, a recently developed model for estimating carbonation depth (using mixture proportion) have been used. Then, the life-cycle assessment (LCA) of these three concrete systems in terms of the CO2 emissions per unit of concrete per year of estimated service life is presented-for both chloride and carbonation induced corrosion. In chloride laden environments, the service life of the bridge pier and girder systems could be enhanced by about 10 times by using fly ash or LC3 concretes-for similar strength grade concretes. Also, the average annual CO2 emissions (during the expected service life) of PFA and LC3 concretes could be about 3 and 7 times, respectively, lower than that of OPC concretes of similar strength grade. In case of carbonation-induced corrosion, the limited experimental data indicate that the PFA and LC3 concretes could exhibit a lower service life and higher average annual CO2 emissions (during the expected service life) than OPC concretes.</p
Residual service life estimation and its importance for pretensioned concrete (PTC) bridges in coastal cities
No full textMany pre-tensioned concrete (PTC) bridges are experiencing premature chloride-induced corrosion. Hence, it is crucial to estimate their residual service life and update it with newer data on a periodic basis-to plan for corrosion prevention or control measures and ensure safety of existing bridges. Critical chloride threshold (Cl th) is one of the parameters necessary to estimate the corrosion initiation period. However, quantitative estimates on Clth for prestressing (PS) steel are not well-reported in literature. This paper presents experimental data on the Clth of PS steel, the chloride diffusion coefficient (Dcl), and surface chloride concentration (Cs) of concrete samples obtained from a PTC bridge girder in a coastal city in India. For estimation of Cl th, 5 specimens were cast with PS steel wires embedded in ordinary Portland cement (OPC) mortar containing 30% of Class F fly ash (similar composition as that of the bridge girder). They were cured for 28 days and then subjected to cyclic wet-dry exposure using simulated concrete pore solution containing 3.5%sodium chloride. (Linear polarization resistance (LPR) tests were performed at the end of each exposure cycle, corrosion initiation was detected using statistical methods, and Clth was determined). Using the determined Clth and Dcl, and other relevant parameters, the cumulative distribution functions of time to corrosion initiation was developed. It was found that the average time to corrosion initiation was about 40 years, whereas the structure was designed for 120 years. Also, it was estimated that the corrosion products will accumulate within the interstitial space between the 7 wires in a strand and will not flow through the concrete cover and reach the concrete surface (showing rust stains) until about 5% of strand is corroded (about 10 years). This indicates a dire need for regular data collection, updating the residual life estimates, which will help in developing corrosion prevention strategies for PTC structures.</p
Residual service life estimation and its importance for pretensioned concrete (PTC) bridges in coastal cities
No full textMany pre-tensioned concrete (PTC) bridges are experiencing premature chloride-induced corrosion. Hence, it is crucial to estimate their residual service life and update it with newer data on a periodic basis-to plan for corrosion prevention or control measures and ensure safety of existing bridges. Critical chloride threshold (Cl th) is one of the parameters necessary to estimate the corrosion initiation period. However, quantitative estimates on Clth for prestressing (PS) steel are not well-reported in literature. This paper presents experimental data on the Clth of PS steel, the chloride diffusion coefficient (Dcl), and surface chloride concentration (Cs) of concrete samples obtained from a PTC bridge girder in a coastal city in India. For estimation of Cl th, 5 specimens were cast with PS steel wires embedded in ordinary Portland cement (OPC) mortar containing 30% of Class F fly ash (similar composition as that of the bridge girder). They were cured for 28 days and then subjected to cyclic wet-dry exposure using simulated concrete pore solution containing 3.5%sodium chloride. (Linear polarization resistance (LPR) tests were performed at the end of each exposure cycle, corrosion initiation was detected using statistical methods, and Clth was determined). Using the determined Clth and Dcl, and other relevant parameters, the cumulative distribution functions of time to corrosion initiation was developed. It was found that the average time to corrosion initiation was about 40 years, whereas the structure was designed for 120 years. Also, it was estimated that the corrosion products will accumulate within the interstitial space between the 7 wires in a strand and will not flow through the concrete cover and reach the concrete surface (showing rust stains) until about 5% of strand is corroded (about 10 years). This indicates a dire need for regular data collection, updating the residual life estimates, which will help in developing corrosion prevention strategies for PTC structures.</p
Experimental and numerical investigation on the irregularity of carbonation depth of concrete under supercritical condition
No full textThe heterogeneity of a cement-based material results in a random spatial distribution of carbonation depth, which may significantly affect the mechanical properties and durability of the material. Currently, there is a lack of both experimental and numerical investigations aiming at a statistical understanding of this important phenomenon. This paper presents both experimental and numerical supercritical carbonation results of concrete blocks. The random fields of porosity and two-dimension random aggregate model of concrete were proposed for the simulation. The carbonation depths are measured and distributed along the carbonation boundary by the proposed rapid image processing technique, which are then statistically studied. The study has shown that considering the random distribution of coarse aggregates and using a random field of porosity with due consideration of spatial correlation and variance, the irregularity of carbonation depth can be realistically captured by the numerical model. Overall the methodology adopted in the paper can provide a foundation for future investigations on probability analysis of carbonation depth and other similar work based on multi-scale and-physics modelling
A novel assessment of the electrochemical lithium impregnation treatment used to mitigate alkali-silica reaction in concrete
No full textLithium compounds are used to prevent alkali–silica reaction (ASR) in concrete. If lithium is mixed in wet concrete, the swelling effects of ASR are mitigated. Electrochemical lithium impregnation techniques have been also used successfully on a number of older structures. This paper evaluates the electrochemical penetra-tion and ASR performance of lithium in hardened concrete. Reactive Colombian aggregate and commercial cement were used to prepare mortar mixes and lithium nitrate performance was evaluated using the accelerat-ed ASTM C1260 Mortar-Bar Method. Two penetration methods were used to introduce lithium into concrete. First, concrete was mixed with lithium in the mix water and expansion was measured using ASTM C1260. Second, lithium ions were migrated into ASTM 1260 mortar bars using an electric field.A novel experimental method was developed for electrochemical treatment and assessment of the mortar bars. Samples were cast in ASTM C490 molds used in determining the length change of mortar bars (25 x 25 x 250mm). Stainless steel electrodes were used in the migration cells, which were filled using 0.3M KOH + 0.1M NaOH in the cathode reservoir and 30% LiNO3 in the anode reservoir. Voltages of 15 and 20 Volts were applied for 4 days. After electrochemical treatment, samples were tested to ASTM C1260. Compressive strength tests were carried out to determine the effects of lithium. Results indicate that lithium significantly mitigates the reactivity of aggregate and the ionic lithium migration seems to be more effective than initial mixing
Monitoring the development of microcracks in reinforced concrete caused by sustained loading and chloride induced corrosion
No full textChloride-induced corrosion of steel in reinforced concrete structures is one of the main problems affecting their durability and it has been studied for decades, but most of them have focused on concrete without cracking or not subjected to any structural load. In fact, concrete structures are subjected to various types of loads, which lead to cracking when the tensile stress in concrete exceeds its tensile strength. Cracking could increase transport properties of concrete and accelerate the ingress of harmful substances (Cl -, O2, H2 O, CO2). This could initiate and accelerate different types of deterioration processes in concrete, including corrosion of steel reinforcement. The expansive products generated by the deterioration processes themselves can initiate cracking. The success of concrete patch repairs can also influence microcracking at the interface as well as the patch repair itself. Therefore, monitoring the development of microcracking in reinforced concrete members is extremely useful to assess the defects and deterioration in concrete structures. In this paper, concrete beams made using 4 different mixes were subjected to three levels of sustained lateral loading (0%, 50% and 100% of the load that can induce a crack with width of 0.1mmon the tension surface of beams - F 0.1) and weekly cycles of wetting (1 day)/drying (6 days) with chloride solution. The development of microcracking on the surface of concrete was monitored using the Autoclam Permeability System at every two weeks for 60 weeks. The ultrasonic pulse velocity of the concrete was also measured along the beam by using the indirect method during the test period. The results indicated that the Autoclam Permeability System was able to detect the development of microcracks caused by both sustained loading and chloride induced corrosion of steel in concrete. However, this was not the case with the ultrasonic method used in the work (indirect method applied along the beam); it was sensitive to microcracking caused by sustained loading but not due to corrosion.</p
E-journals in a networked environment : its impact on academic libraries in the digital millennium
No full textThis paper tries to describe the Advantages of E-journals in terms of Accessibility, Speed distribution and production, Subscription Cost, Multimedia Capabilities, Internal and External Links etc and also tries to find out the Technological, Socio-cultural and Economic Barriers. The issues like Refereeing, Copyright and Licensing, Longevity and Storage and recent trends in E-journal publication and its implication on Academic Libraries in selection and acquisition, Cataloguing, archiving, user's access, training and support to staff and users are discussed in this paper
Maturity testing of lightweight self-compacting and vibrated concretes
No full textA series of laboratory tests were carried out to investigate the effect of temperature on the early-age strength development of lightweight self-compacting and vibrated concrete mixtures. These had been developed at Queen’s University Belfast as part of a Technology Strategy Board funded project aimed at developing lightweight and low energy concretes. The new mixtures incorporated high volumes of pulverised fuel ash (PFA), ground granulated blast furnace slag (GGBS), and limestone powder (LSP). Activator, i.e. sodium sulphate, was used to improve the early age strength development of vibrated concrete mixtures proportioned with PFA and GGBS. For each mixture, concrete cubes were manufactured and cured under isothermal (20 °C, 30 °C, 40 °C and 50 °C) as well as adiabatic conditions. The temperature rise under adiabatic curing conditions was also measured. The resulting isothermal strength data were analysed to determine the apparent activation energies of the binders/mixtures used. The suitability of maturity methods for predicting concrete strength development of these low energy lightweight self-compacting and vibrated concrete mixtures under non-isothermal, i.e. adiabatic, curing was assessed
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