• Energy Research

Depending on the availability of aggregate sources pertaining to their geographic locations, the concrete industry utilizes conventional aggregates such as marine sand, dredged gravel, or crushed rocks. This method requires high energy and high processing costs for washing and grinding. The objective of this work is to use Modified Ferro silicate slag (MFS), a by-product obtained from the copper industry, as an alternative to the conventional fine aggregates found in mortar. No additional processing such as washing or grinding is required. By using the MFS slag as an aggregate in mortar or concrete, the factors of sustainability and a circular economy are enhanced. The current study focuses on the characterization of the MFS slag, including the mortar mixes with the MFS slag as a fine aggregate, and shows that the MFS slag can be a promising raw material to replace conventional aggregates in mortar. The leaching of its heavy elements such as Sb, As, Cr, Mo, Pb, and Zn was conducted well within limits (VLAREMA 4). The SEM and MIP analyses indicated that the porosity of the MFS slag mortar was higher compared to the standard aggregate mortar. Moreover, the MFS slag mortar showed acceptable resistance toward the alkali-silica reaction and carbonation.

Depending on the availability of aggregate sources pertaining to their geographic locations, the concrete industry utilizes conventional aggregates such as marine sand, dredged gravel, or crushed rocks. This method requires high energy and high processing costs for washing and grinding. The objective of this work is to use Modified Ferro silicate slag (MFS), a by-product obtained from the copper industry, as an alternative to the conventional fine aggregates found in mortar. No additional processing such as washing or grinding is required. By using the MFS slag as an aggregate in mortar or concrete, the factors of sustainability and a circular economy are enhanced. The current study focuses on the characterization of the MFS slag, including the mortar mixes with the MFS slag as a fine aggregate, and shows that the MFS slag can be a promising raw material to replace conventional aggregates in mortar. The leaching of its heavy elements such as Sb, As, Cr, Mo, Pb, and Zn was conducted well within limits (VLAREMA 4). The SEM and MIP analyses indicated that the porosity of the MFS slag mortar was higher compared to the standard aggregate mortar. Moreover, the MFS slag mortar showed acceptable resistance toward the alkali-silica reaction and carbonation.

[EN] The appearance of cracks in structural reinforced concrete is inevitable and when out of control, it can be the cause of concrete failure. The ingress of water and harmful substances via the cracks is critical as the embedded steel reinforcements in the concrete can be corroded. Crack formation will directly weaken the bond between the reinforcing bar and concrete. To mitigate this issue, cracks should be repaired and closed relatively fast and this can potentially be obtained by incorporating self-healing technologies. Self-healing concrete demonstrates a good healing efficiency by the use of smart materials which allow for autonomous healing or enhance the autogenous healing mechanism of concrete. However, it is questioned whether the precipitates only artificially close the crack or also contribute to improve the bond with the reinforcement. In this study, an experimental investigation was conducted to evaluate the bond properties of self-healing concrete by means of pull-out tests. Four types of healing agents were used including two non-axenic biomass agents (HTN and YEAST) and two commercial agents (crystalline admixture and bacteria (CA and BAC)). The fresh properties and mechanical properties of the concrete including the healing agents were initially investigated. Pull-out tests were executed on uncracked, cracked and healed specimens. Two healing periods (28 and 112 days water immersion) were considered to evaluate the effect of healing time on bond recovery. Test results confirm that the addition of healing agents induced a better improvement of bond properties of steel reinforcement in uncracked concretes with respect to the reference concrete (no healing agent added). The highest bond strength enhancement by 57% on uncracked concrete was obtained with the addition of CA, while the inclusion of other agents such BAC, HTN and YEAST also possessed the bond strength improvement by 47, 21 and 7%, respectively. The presence of a longitudinal crack in concrete significantly reduced the bond strength up to 80% and this effect was not significantly affected by the crack size, when considering cracks in the range of 200¿500 µm, and the introduction of healing agents. Nevertheless, the bond properties were slightly recovered after healing due to self-healing effects and formation of healing products in the crack was clearly visible. This project has received funding from the European Union s Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant agreement No 860006.

[EN] The appearance of cracks in structural reinforced concrete is inevitable and when out of control, it can be the cause of concrete failure. The ingress of water and harmful substances via the cracks is critical as the embedded steel reinforcements in the concrete can be corroded. Crack formation will directly weaken the bond between the reinforcing bar and concrete. To mitigate this issue, cracks should be repaired and closed relatively fast and this can potentially be obtained by incorporating self-healing technologies. Self-healing concrete demonstrates a good healing efficiency by the use of smart materials which allow for autonomous healing or enhance the autogenous healing mechanism of concrete. However, it is questioned whether the precipitates only artificially close the crack or also contribute to improve the bond with the reinforcement. In this study, an experimental investigation was conducted to evaluate the bond properties of self-healing concrete by means of pull-out tests. Four types of healing agents were used including two non-axenic biomass agents (HTN and YEAST) and two commercial agents (crystalline admixture and bacteria (CA and BAC)). The fresh properties and mechanical properties of the concrete including the healing agents were initially investigated. Pull-out tests were executed on uncracked, cracked and healed specimens. Two healing periods (28 and 112 days water immersion) were considered to evaluate the effect of healing time on bond recovery. Test results confirm that the addition of healing agents induced a better improvement of bond properties of steel reinforcement in uncracked concretes with respect to the reference concrete (no healing agent added). The highest bond strength enhancement by 57% on uncracked concrete was obtained with the addition of CA, while the inclusion of other agents such BAC, HTN and YEAST also possessed the bond strength improvement by 47, 21 and 7%, respectively. The presence of a longitudinal crack in concrete significantly reduced the bond strength up to 80% and this effect was not significantly affected by the crack size, when considering cracks in the range of 200¿500 µm, and the introduction of healing agents. Nevertheless, the bond properties were slightly recovered after healing due to self-healing effects and formation of healing products in the crack was clearly visible. This project has received funding from the European Union s Horizon 2020 research and innovation programme under the Marie Skodowska-Curie grant agreement No 860006.

Partially substituting Portland cement (PC) with waste brick powder (WBP) is an effective method to reduce environmental pollution. In this paper, the effects of a WBP with low pozzolanic activity on the fresh and hardened properties of blended cement with 0–40% WBP or 50% of WBP+GGBFS (by mass) were studied. Sodium sulphate (SS) (1.5 and 2.5%, related to powder mass) was used to activate the blended cement with 40% WBP or 50% WBP+GGBFS at 20 °C. Results show that the performance of blended cement is decreased with the increase in WBP content since the WBP with low pozzolanic activity mainly contributes to the dilution effect. Binary cement with 10% WBP shows a similar carbonation depth and chloride migration coefficient to PC. Ternary cement with 10% WBP and 40% GGBFS exhibits a slightly lower strength at 90 days and a lower chloride migration coefficient than PC. The SS solution increases the compressive strength at 2 days and decreases the compressive strength at 28 and 90 days. Moreover, the SS solution results in a lower carbonation depth and chloride migration coefficient, except for ternary cement with 10% WBP and 40% GGBFS, which shows a higher carbonation depth at 42 and 68 days. This paper provides a reference for the application of WBP to produce green mortars.

Partially substituting Portland cement (PC) with waste brick powder (WBP) is an effective method to reduce environmental pollution. In this paper, the effects of a WBP with low pozzolanic activity on the fresh and hardened properties of blended cement with 0–40% WBP or 50% of WBP+GGBFS (by mass) were studied. Sodium sulphate (SS) (1.5 and 2.5%, related to powder mass) was used to activate the blended cement with 40% WBP or 50% WBP+GGBFS at 20 °C. Results show that the performance of blended cement is decreased with the increase in WBP content since the WBP with low pozzolanic activity mainly contributes to the dilution effect. Binary cement with 10% WBP shows a similar carbonation depth and chloride migration coefficient to PC. Ternary cement with 10% WBP and 40% GGBFS exhibits a slightly lower strength at 90 days and a lower chloride migration coefficient than PC. The SS solution increases the compressive strength at 2 days and decreases the compressive strength at 28 and 90 days. Moreover, the SS solution results in a lower carbonation depth and chloride migration coefficient, except for ternary cement with 10% WBP and 40% GGBFS, which shows a higher carbonation depth at 42 and 68 days. This paper provides a reference for the application of WBP to produce green mortars.

Novel hybrid binder concrete mixes with alkali-activated non-ferrous slag (NFS), either alone or in combination with blast furnace slag (BFS), as partial replacement of Portland cement, and containing 50% recycled aggregates, were successfully manufactured. The compressive strength, carbonation resistance, chloride resistance, frost scaling, sorptivity coefficient, and water penetration resistance were thoroughly assessed. The presence of recycled aggregates had an adverse effect on early-age strength, but after 91 days there was no difference between concrete with and without recycled aggregates. The chloride-binding capacity was enhanced in the BFS/NFS system with recycled aggregates (reduction in chloride ingress coefficients of ~28–35% compared to recycled concrete with NFS only). This is most likely caused by the binding of Cl ions in calcium alumina silicate hydrates (C-A-S-H) and ettringite phases. However, when compared to the system with virgin aggregates, BFS/NFS concrete with recycled aggregates showed increased carbonation rate (+30%) and frost scaling (+15%). Durability properties, such as sorptivity and water penetration resistance, were positively affected by the curing time for the BFS/NFS system (~35–45% further improvement from 28 to 90 days with respect to the NFS system). Specimens that were wet cured for 91 days showed improved results compared to the 28-day cured samples due to the slow pozzolanic reaction of the NFS.

Novel hybrid binder concrete mixes with alkali-activated non-ferrous slag (NFS), either alone or in combination with blast furnace slag (BFS), as partial replacement of Portland cement, and containing 50% recycled aggregates, were successfully manufactured. The compressive strength, carbonation resistance, chloride resistance, frost scaling, sorptivity coefficient, and water penetration resistance were thoroughly assessed. The presence of recycled aggregates had an adverse effect on early-age strength, but after 91 days there was no difference between concrete with and without recycled aggregates. The chloride-binding capacity was enhanced in the BFS/NFS system with recycled aggregates (reduction in chloride ingress coefficients of ~28–35% compared to recycled concrete with NFS only). This is most likely caused by the binding of Cl ions in calcium alumina silicate hydrates (C-A-S-H) and ettringite phases. However, when compared to the system with virgin aggregates, BFS/NFS concrete with recycled aggregates showed increased carbonation rate (+30%) and frost scaling (+15%). Durability properties, such as sorptivity and water penetration resistance, were positively affected by the curing time for the BFS/NFS system (~35–45% further improvement from 28 to 90 days with respect to the NFS system). Specimens that were wet cured for 91 days showed improved results compared to the 28-day cured samples due to the slow pozzolanic reaction of the NFS.