International Concrete Abstracts Portal

A novel technique to upgrade the mortar durability by surface coating layer formation and densification using an electrodeposition method is suggested here. In this technique, the SiO32- ions as key raw materials are applied. Under the applied electric field, they are transported into the pores to react with Ca(OH)2 to promote the additional C-S-H gel formation, which induces the densification of mortar. Besides, the accelerated hydrolytic reaction of SiO32- ions, and the reaction of SiO32- ions in the outer electrolyte with the leached Ca2+ promote C-S-H/silica gel precipitation on the mortar surface. Furthermore, by a comparative experiment, it has been found that this technique can moderately increase the compressive strength and flexural strength of electrodeposited mortar sample. Also, the chloride diffusion into the electrodeposited mortar sample is notably decreased, which demonstrates the effectiveness of this electrodeposition technique in upgrading the durability.

The effects of substituting 5-20% fly ash for slag and adding 0.10~0.30% polypropylene fiber on the physical and mechanica1 properties, shrinkage and cracking behaviors, water permeability and porosity of alkali-activated ground granulated blast furnace slag cement paste and mortar are studied. The results show that replacing 5-15% fly ash for slag in the alkali-activated slag cement paste and mortar increased the flexural strength, though the compressive strength were slightly decreased. When the replacement of fly ash for slag was increased to 20%, both the flexural and compressive strengths of the paste and mortar begin to decrease. The early shrinkage and cracking were reduced by the fly ash replacement. Adding 0.10~0.30% polypropylene fiber decreased both the flexural and compressive strengths, whereas the shrinkage, especially the cracking of the alkali-activated slag cement was greatly reduced.

The research aims at studying an innovative construction system (called S.E.Con. System1 - Sustainable Ecological Construction System) to realize sustainable buildings, having both acoustic and thermal high performance, in which the seismic-resistant structural elements are small reinforced concrete walls widely spread on the perimeter of the building and where all vertical structural and secondary elements (infill panels) are constructed using shotcrete. The results of experimental tests on a single story sample building and on structural walls, aimed to assess the structural, acoustic, and thermal insulation performances of the devised system, demonstrate that the system appears suitable for high seismicity areas, and that thermal and acoustic criteria set for passive constructions are met. Finally, an evaluation of the carbon footprint (CFP) has also been carried out, demonstrating a reduction of about 30% in the CFP of the construction system with respect to traditional construction systems.

The demand for the development of a more efficient and durable transportation infrastructure is among the top priorities of highway authorities worldwide. In the United States, the economic impact of steel corrosion for concrete highway bridges is estimated to exceed 15 percent of total annual costs. Degradation affecting steel reinforced concrete (RC) bridge superstructures exposed to harsh environmental conditions is not limited to decks, but includes railings and barriers and can significantly compromise their crashworthiness. Glass fiber reinforced polymer (GFRP) is highly suitable for reinforcing concrete structures subjected to corrosive environments and a number of projects have demonstrated its viability as an alternative reinforcement for bridge decks. Until recently, most traffic barriers using GFRP bars were vertical-faced systems. However, the impact time duration of vertical-faced barriers is shorter causing higher peak forces to be transferred to vehicle occupants. Nowadays, GFRP manufacturers can produce standard bar bends which can be used for the reinforcement of safety-shaped concrete railings and barriers. The implementation of GFRP bar bends requires some changes in the current design philosophy for railings and barriers. Whereas the overall goal of the research program is to make the technology of concrete bridge reinforcement with composites available to bridge owners and professionals, this paper provides the principles for the design of safety-shaped GFRP-reinforced concrete railings/barriers.

Diffusion and migration are the two major transport ways of chloride ions in concrete. The single-species models were usually used to predict the chloride diffusion and migration behavior. However, the diffusion and migration processes of chloride ions in concrete are more complicated than expected. The single-species models have obvious limitations in predicting the diffusion and migration processes. In this paper, two multi ionic models are introduced to predict the chloride diffusion and migration processes, respectively. In the diffusion model, the ionic actions and multi-phase reactions are both considered in order to simulate the realistic situations. In the migration model, the ionic actions are also considered while the multi-phase reactions are ignored due to the strong electrical field force applied in the migration test. Besides, a pore structure hypothesis is assumed by a simple deduction to distinguish the migration process from the diffusion process. By considering the factors mentioned above, the governing equations of diffusion and migration models are deduced respectively. In order to verify the multi ionic models, two numerical examples and the verification tests are also conducted. The results show that the multi-ionic models are feasible to predict the chloride diffusion and migration in concrete.