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Abstract Autogenous crack healing can be stimulated with superabsorbent polymers (SAPs) in microfibre reinforced strain hardening engineered cementitious composite (ECC). Cradle-to-gate life cycle assessment was performed for self-healing ECC with 1 m% of three in-house developed (semi-)synthetic SAPs and 2 v% of polypropylene (PP) or polyvinyl alcohol (PVA) microfibre. Given the high cement content of this ECC (572 kg/m3), CML-IA impacts of 1 m% SAP range between 4 and 52% of the cement impact. The highest impacts were recorded for semi-synthetic SAPs, due to high energy use during drying. Use of PVA microfibre should be avoided since addition of 2 v% (= 26 kg/m3) can easily induce significantly higher CML-IA impacts than 572 kg cement. Nonetheless, if 100% crack healing efficiency could be assumed for slabs made of self-healing ECC, CML-IA impacts remain lower than those of a slab made of traditional concrete with inclusion of the required cover replacements within 100 years. [ABSTRACT FROM AUTHOR]

Today, it remains unclear how ‘green’ concrete with high volumes of fly ash really is, especially when subject to chloride-induced corrosion. This paper presents chloride diffusion test results for high-volume fly ash and fly ash + silica fume concrete. Apparent diffusion coefficients and surface concentrations were compared with those for traditional concrete. Instantaneous chloride diffusion coefficients and ageing exponents were estimated and critical chloride contents for submerged exposure conditions were experimentally verified. The estimated time to chloride-induced steel depassivation for the two concrete types with fly ash (60 to more than 100 years) was much longer than for traditional concrete (24–32 years). As a consequence, global warming potentials (GWPs) calculated for the required concrete volume per unit of strength and service life indicate that an important reduction in greenhouse gas emissions is possible for both concrete types with high volumes of fly ash (GWP –50 to −82%). [ABSTRACT FROM AUTHOR]

The carbonation behavior of concrete with different blast furnace slag replacement ratios (0 %, 50 % and 70 %) at different CO 2 concentrations (natural carbonation at 0.04 % and accelerated carbonation at 1 % and 2 %) was investigated in terms of carbonation rate, carbonation products assemblage and pore structure. The results show that the porosity of concrete decreases with the increase in CO 2 concentration regardless of mix proportion. The lower porosity at a higher CO 2 concentration can lead to an underestimation of the natural carbonation coefficient from accelerated carbonation tests. The carbonation degree of the C-S-H is one of the key factors that determine the carbonation behavior at different CO 2 concentrations. A higher CO 2 concentration enhances the consumption of the high-density C-S-H and therefore the carbonation of unreacted clinker. However, the C-S-H formed from GGBFS hydration is carbonated to a more advanced state (considerable silica gel is formed) under natural carbonation. • Densification by carbonation can cause underestimation of natural carbonation rate. • CO 2 concentration influences the carbonation degree of hydration products differently. • Carbonation degree of C-S-H is more uneven under natural carbonation. • Accelerated carbonation at a higher CO 2 concentration densifies the pore structure. [ABSTRACT FROM AUTHOR]

• Carbonation rate of concrete under uniaxial compressive load was tested. • Carbonation resistance of BFS concrete is improved by compressive service load. • Microcrack healing and pore densification caused the slower carbonation under load. • Crack propagation caused the faster carbonation above the threshold load level. Carbonation of concrete, in which 0%, 50% and 70% of cement was replaced by blast furnace slag (BFS), under different levels of sustained compressive load (0, 0.25, 0.5 and 0.75 times the breaking load) was investigated. The results show that the carbonation rate first decreases with load level and then above a threshold value (approximately 0.25–0.5 times the breaking load) increases with load level. The carbonation rate of BFS concrete becomes closer to that of Portland cement concrete under sustained compressive load. An investigation of the load-induced microstructure changes showed that the densification effect dominates in the carbonated zone in terms of lower porosity, denser interfacial transition zone, lower crack width and autogenous healing of fine cracks. The cracking effect plays a more significant role in the non-carbonated zone and leads to a notable increase in the carbonation rate at a high load level. The average major principle strain obtained by digital image correlation can be used to evaluate the combined effect of densification and cracking. [ABSTRACT FROM AUTHOR]

Abstract: Concrete containing supplementary cementitious materials as, e.g. fly-ash (FA) or blast-furnace slag (BFS) is more vulnerable to carbonation than ordinary Portland cement concrete. In order to know whether carbonation-initiated corrosion is a risk within the life span of the concrete structure, the carbonation depth after several years (e.g. 50years) is mostly predicted based on accelerated carbonation tests on young concrete specimens. However, these predictions do not take into account the positive effect of the continuing hydration of slag and fly-ash particles over a longer time. In this study, accelerated carbonation tests (10vol.% of CO2) were performed on concrete specimens containing different amounts of blast-furnace slag (slag-to-binder ratios of 50%, 70% and 85%) after different curing times (1, 3, 6 or 18months). Based on these tests, a new method, which takes into account the effect of the ongoing hydration, is described in order to predict the carbonation depth of these special types of concrete over a long time more realistically. The tests revealed that, although BFS concrete has a lower carbonation resistance than OPC concrete, the depth of carbonation at the end of the concrete’s life (50years) can still be acceptable in normal environments. [Copyright &y& Elsevier]

Abstract: Replacement of ordinary Portland cement (OPC) by blast-furnace slag (BFS) alters the durability behaviour of concrete. In this research, the influence of BFS on the concrete''s acid or sulphate resistance is investigated by accelerated degradation tests and the results are related to microstructural and physico-chemical parameters. A significant reduction of acid deterioration was recorded for BFS concrete, which is mainly attributed to the different chemical composition of the binder. General durability indicators like open porosity cannot solely explain the different performances of OPC and BFS concrete. In contrast, the resistance of concrete cyclically and partially submerged in sulphate solutions decreases when high amounts of cement are replaced by BFS. Crystallisation pressure causes more severe deterioration in these cases. [Copyright &y& Elsevier]

Binders with large portions of carbon-intensive Portland cement replaced by supplementary cementitious materials (e.g. fly ash) are more susceptible to carbonation mainly due to their lower CO 2 buffering capacity. This conclusion is usually drawn from accelerated experiments at elevated CO 2 levels involving processes that seriously differ from natural carbonation. The resulting presence of H 2 O reactant in the pore system and the carbonated microstructure itself may be very different. In this paper, these phenomena were investigated for High-Volume Fly Ash (HVFA) mortar via carbonation tests at ±0.04% CO 2 (natural carbonation), 1% CO 2 and 10% CO 2. Internal humidity sensor monitoring and 1H NMR relaxometry revealed the highest water vapour and liquid water contents after carbonation at 10% CO 2. Carbonation at 10% CO 2 results in a coarser pore structure than carbonation at 1% CO 2 , and this probably due to a higher degree of C–S–H carbonation. • Internal relative humidity after carbonation is higher at 10% CO 2 than at 1% CO 2. • MRE resistivity after carbonation is lower at 10% CO 2 than at 0.04 and 1% CO 2. • NMR assessed liquid H 2 O content after carbonation is higher at 10% CO 2 than at 1% CO 2. • Coarsening of pore structure after carbonation is higher at 10% CO 2 than at 1% CO 2. • A 10% CO 2 level is too high in view of still assessing natural carbonation phenomena. [ABSTRACT FROM AUTHOR]

Abstract Cracks in reinforced concrete structures accelerate the ingress of chlorides and therefore cause a higher risk for corrosion. In this research, autonomous healing of cracks by encapsulated polyurethane was investigated as a possible method to reduce reinforcement corrosion. Reinforced concrete beams were exposed weekly to a chloride solution and electrochemical parameters were measured to determine the influence of the self-healing mechanism on the corrosion process. The rebars were visually examined afterwards. For the cracked beams an active state of corrosion was detected within an exposure period of 10 weeks and clear pitting corrosion was observed on the rebars. Autonomous crack healing with low viscosity polyurethane could significantly reduce the corrosion in the propagation stage. For these specimens no visual damage to the rebars was detected. In conclusion, the application of self-healing concrete with a low viscosity polyurethane is able to enhance the durability of reinforced concrete structures in marine environments. [ABSTRACT FROM AUTHOR]

Alkali activation may help to increase the early strength and reduce the setting time of mixtures with high contents of supplementary cementitious materials (SCMs). In this research, the effect of sodium sulfate activator on reaction kinetics, compressive strength and pore structure of hybrid systems produced with 70 wt% ground granulated blast furnace slag (GGBFS) and 30 wt% Portland cement (PC) was determined. The setting time was shortened by adding sodium sulfate, but increasing the dose above 3 wt% did not influence it drastically. In-situ XRD measurements revealed an increasing ettringite formation within the first 2 days of hydration. A greater reaction of the GGBFS resulted in a pore refinement of the mortars studied and consequently raised the early age compressive strength. The assessment of a convenient dosage of activator was based on both technological and environmental parameters. The contribution of PC and GGBFS to compressive strength was "decoupled". [ABSTRACT FROM AUTHOR]

During capillary imbibition, there are changes in the pore structure that reduce the water ingress rate, leading to anomalous behaviour. However, the relation of those deformations with the C-S-H content is still unclear. We performed simultaneous measurements of external deformations and water ingress through neutron radiography. Cement pastes of water/cement of 0.4 and 0.6, using both Portland and white cement were tested after 1 year curing. Porosity and calcium silicate hydrate (C-S-H) content of the pastes were determined. Strain gauges were attached perpendicular and parallel to the water flow. Results indicate that the degree of internal restriction of the mix influences the shape of the water profile and that C-S-H deformations affect internal changes more than external. Water ingress visualisation indicated the lack of a sharp front during imbibition and the saturation degree variation at the position of the strain gauges. We propose a model to address the dynamic porosity. [Display omitted] • The water front from neutrographs is linked to a dynamic pore structure. • Porosity and C-S-H content are not isolated factors affecting external deformations. • Ample evidence supports a variable inner pore structure during capillary imbibition. • The usual approach of rigid pore structure during imbibition needs to be abandoned. • The model considers a kinetic variable, based on contact time and saturation degree. [ABSTRACT FROM AUTHOR]

• Perpendicular-to-crack chloride ingress causes a 2D transport phenomenon. • Autonomous crack healing reduces chloride ingress in cracked concrete. • EPMA provides very detailed information on chloride ingress in concrete. • Good correlation between EPMA data and traditional methods. • Self-healing concrete reduces perpendicular-to-crack chloride ingress. The appearance of cracks in reinforced concrete structures accelerates the penetration of aggressive substances such as chloride ions into the concrete matrix. This leads to durability problems due to the accelerated onset of chloride induced reinforcement corrosion. Chloride ions penetrate the concrete matrix along the crack tip and also along the crack walls in a direction perpendicular to the crack. This research focused on the application of autonomous crack healing by encapsulated polyurethane as a method to reduce (perpendicular-to-crack) chloride ingress. Three investigation methods were applied: profiling by grinding followed by potentiometric titration, visualization of the chloride penetration front using AgNO 3 and Electron Probe Micro Analysis (EPMA). The proposed healing mechanism proved to be efficient to reduce the chloride concentrations in the direct vicinity of the crack and to cause a reduction of the perpendicular-to-crack chloride penetration. Furthermore, the results found by the different evaluation methods were comparable to each other. In this sense, the data obtained by EPMA contained most of the information that was obtained by the AgNO 3 spray method and the chloride profiling together. This proves that EPMA is a powerful technique for analyzing the chloride penetration in concrete and a valuable tool to determine the crack healing efficiency of self-healing concrete. [ABSTRACT FROM AUTHOR]

In the context of the rising awareness regarding sustainability, a Belgian producer of high-strength prestressed concrete elements for structural and civil applications aimed to clarify several aspects of ecological certifications and standards, and the application of these items within the company. In a first part of this paper, a life cycle assessment (LCA) for the precast element production up to delivery on site is presented, in which accurate company information and specific data from internal and external databases is used. The LCA determines that although reinforcing steel and cement dominate the impact contributions, other factors such as transport by road, maintenance, aggregates, element fabrication and concrete waste are non-negligible. Subsequently, a study of an ecological variant, presented in the second part of this paper, shows that several adaptions within the manufacturing process can potentially reduce the impact on the environment with 20–30%, depending on the assessment method used. [ABSTRACT FROM AUTHOR]

• A joint simulation of 2 FEM software is used to predict the carbonation depth. • The model is modified to consider the effect of stress and damage on diffusivity. • The effect of the uniaxial compressive load is determined by a comparative test. • The multiaxial strength and load level in each element are determined. A numerical method is proposed to determine the semi-carbonated and fully-carbonated depth of concrete subjected to sustained loads. The method modified the diffusivity of each element by multi-axial load levels and stress damages. Based on 1000-day carbonation results of 2D mesoscale concrete, it was indicated that the external load causes highly uneven carbonations and has a similar influence on the semi-carbonated and fully-carbonated depth. However, the tensile and compressive loads have distinctly different influences. Moreover, the relationship between carbonation depths and exposure times which is consistent with Fick's first law will be broken in the post-peak segment due to severe damages' propagation. [ABSTRACT FROM AUTHOR]

Due to the increasing awareness and sensitivity towards the environmental and economic sustainability issues, the concrete industry has to deliver innovative solutions, in terms of materials, products and structural concepts, to achieve higher durability of engineering feats in real service scenarios. The inclusion of SuperAbsorbent Polymers (SAPs) into the concrete mix, can not only stimulate the autogenous crack healing, but is also able to reduce the shrinkage cracking through internal curing. In this paper, Life Cycle Assessment (LCA) and Life Cycle Cost (LCC) analysis have been performed to assess both the ecological and economic profile, in real scale, of conventional reinforced concrete structures, made with concrete containing SAPs, in comparison to a reference solution without any addition. For this purpose, the corrosion of reinforcement has been regarded as the main degradation mechanism and different corrosion models have been considered and combined with the structural analysis principles to obtain reliable Service Life (SL) estimations. Four different scenarios, with a SL ranging from 50 up to 100 years, have been analyzed to assess the potential benefits of a wall, cast with SAP-containing concrete (Wall_SAP). Both Wall_SAP and a reference wall without SAP (Wall_Ref) are subjected to the concrete cover replacement as main maintenance activity while for the Wall_Ref also the crack filling by means of polyurethane resin is considered as an option (Wall_Resin). The adopted CML impact-assessment method, developed by the Center of Environmental Science of Leiden University, shows the advantage of using SAPs, since the environmental burdens were reduced up to 20% in the case of Fresh Water Aquatic Ecotoxicity impact category in comparison to the reference for the fourth scenario. In this scenario a hemispherical corrosion pit model for the steel bars and a service life of 100 years were taken into account. Furthermore, the economic assessment developed for the same scenario, pointed out for the SAPs based solution, there identified as Wall_SAP_M2_100, a consistent reduction in terms of costs up to 14% if compared to the reference, there named as Wall_Ref_M2_100. The outcomes definitely highlight the potential of the analyzed technology that can fulfil the future needs of the stakeholders involved in the construction sector. [ABSTRACT FROM AUTHOR]