Bjorn Van Belleghem

Neutron Radiography Based Visualization and Profiling of Water Uptake in (Un)cracked and Autonomously Healed Cementitious Materials

Given their low tensile strength, cement-based materials are very susceptible to cracking. These cracks serve as preferential pathways for corrosion inducing substances. For large concrete infrastructure works, currently available time-consuming manual repair techniques are not always an option. Often, one simply cannot reach the damaged areas and when making those areas accessible anyway (e.g., by redirecting traffic), the economic impacts involved would be enormous. Under those circumstances, it might be useful to have concrete with an embedded autonomous healing mechanism. In this paper, the effectiveness of incorporating encapsulated high and low viscosity polyurethane-based healing agents to ensure (multiple) crack healing has been investigated by means of capillary absorption tests on mortar while monitoring the time-dependent water ingress with neutron radiography. Overall visual interpretation and water front/sample cross-section area ratios as well as water profiles representing the area around the crack and their integrals do not show a preference for the high or low viscosity healing agent. Another observation is that in presence of two cracks, only one is properly healed, especially when using the latter healing agent. Exposure to water immediately after release of the healing agent stimulates the foaming reaction of the polyurethane and ensures a better crack closure.

Quantification of the Service Life Extension and Environmental Benefit of Chloride Exposed Self-Healing Concrete

Formation of cracks impairs the durability of concrete elements. Corrosion inducing substances, such as chlorides, can enter the matrix through these cracks and cause steel reinforcement corrosion and concrete degradation. Self-repair of concrete cracks is an innovative technique which has been studied extensively during the past decade and which may help to increase the sustainability of concrete. However, the experiments conducted until now did not allow for an assessment of the service life extension possible with self-healing concrete in comparison with traditional (cracked) concrete. In this research, a service life prediction of self-healing concrete was done based on input from chloride diffusion tests. Self-healing of cracks with encapsulated polyurethane precursor formed a partial barrier against immediate ingress of chlorides through the cracks. Application of self-healing concrete was able to reduce the chloride concentration in a cracked zone by 75% or more. As a result, service life of steel reinforced self-healing concrete slabs in marine environments could amount to 60–94 years as opposed to only seven years for ordinary (cracked) concrete. Subsequent life cycle assessment calculations indicated important environmental benefits (56%–75%) for the ten CML-IA (Center of Environmental Science of Leiden University–Impact Assessment) baseline impact indicators which are mainly induced by the achievable service life extension.

Screening of Different Encapsulated Polymer-Based Healing Agents for Chloride Exposed Self-Healing Concrete Using Chloride Migration Tests

The service life of steel reinforced concrete in aggressive marine environments could be increased substantially by embedding a self-healing mechanism that ensures autonomous healing of cracks upon their occurrence. Previous proof-of-concept experiments have shown that the incorporation of encapsulated polymer-based healing agents (HAs) counts as a very appropriate way to achieve this goal. Over the years, several polymer-precursor-capsule systems have been developed in that perspective at our laboratory. Cementitious materials containing either commercial or in-house developed encapsulated HAs have been subjected to preliminary feasibility tests (water absorption, permeability tests, etc.). However, these experiments did not yet allow for a fast and straightforward assessment of the self-healing efficiency (SHE) in relation to the expected durability and service life performance of the material. This approach would have many advantages when having to select the most suitable polymer-precursor-capsule system for a particular concrete application. In this paper, a modified chloride migration test based on the one prescribed in NT Build 492 has been proposed to support the development of self-healing concrete for marine environments. Four polymer-based HAs have been screened that way, i.e. an in-house developed high-viscosity polyurethane (PU) precursor, a commercial low-viscosity PU precursor, the same commercial PU precursor with addition of accelerator and benzoyl peroxide (BPO), and an in-house developed 2-component acrylate-endcapped precursor + cross-linker. For now, a highly repeatable SHE value of 100% could only be obtained for the second option.

Screening Encapsulated Polymeric Healing Agents for Carbonation-Exposed Self-Healing Concrete, Service Life Extension, and Environmental Benefit

By incorporating encapsulated polymers in concrete, cracks can be healed autonomously upon occurrence. This is of high value for steel reinforced concrete structures subject to carbonation-induced corrosion. This paper presents the results of a rapid colorimetric screening test to assess the carbonation resistance of self-healing concretes containing encapsulated polymer-based healing agents. Four systems were tested for inhibition of further carbonation near artificially induced cracks (width: 300 μm). Next, the time to steel depassivation was assessed probabilistically in comparison with cracked concrete. With an adequately working pressurized PU precursor, the concrete would remain repair-free for at least 100 years. Subsequent life cycle assessment in SimaPro showed a potential environmental benefit (72–78%) for the ten CML-IA baseline impact categories which is mainly due to the service life extension possible with a properly working self-healing concrete.

The cost and environmental impact of service life extening self-healing engineered materials for sustainable steel reinforced concrete

To achieve higher sustainability of steel reinforced concrete structures, their service life should be extended. When subject to chloride induced steel corrosion, time dependent repair works are most probably inevitable. Evidently, this results in extra concrete manufacturing and thus more environmental impact. Cracks offering direct pathways for the corrosion inducing substances play a very detrimental role in this. This paper presents the potential of using self-healing concrete to cope with this problem. By incorporating a polyurethane (PU)-based healing agent that is adequately released upon crack occurrence, chloride ingress is hindered substantially and onset of active corrosion is postponed. The required number of repair actions within 100 years could then drop to zero. Nevertheless, the implementation of a self-healing mechanism comes along with a higher initial cost and additional environmental impacts. Therefore, the necessary cost and life cycle assessment calculations have been performed as well. It was found that the cost of the PU-based healing agent is very reasonable while the extra costs of the capsules are for the moment still unacceptable. Environmental burdens associated with the PU precursor filled capsules are negligible (0.1-4.8%) in comparison with the impacts related to regular concrete repair to meet the design service life of 100 years.Concrete is the most manmade material solution produced and used worldwide. Its cornerstone is the cement composite due to the high emissions level and resources consumption volume. Roughly 5-7% of global carbon dioxide emissions come from cement manufacture process. The far-reaching alternative of replacement a clinker portion in the cement material composition has gained consensus. It becomes relevant in emerging economies since in the short-run there is not widely available ways for increasing the production capacity while diminish the environmental impact with no additional investment cost. Low carbon cement (LC3) is leading the contemporary paths towards facing environmental challenges and resource scarcity. This article aims at assessing the theoretical consideration of replacement of the Cuban traditional cements by LC3 according to housing case studies in Villa Clara province. On the basis of LCA background and the supply chain rationale, a procedure for discussing sustainable contribution of LC3 is designed and applied. Hollow blocks and mortars have been included in the calculations as well as the manufacturing/transportation processes for the entire supply chain of one semi-detached two-storey row houses built in the core of a slum-like settlement at Condado suburb-Santa Clara city. This approach demonstrates that the LC3 incorporation in the Cuban construction sector could afford considerable economic savings with the subsequent contribution in favour of the environment.Net zero energy is already an ambitious target for several buildings, especially since the DIRECTIVE 2010/31/EU that requires increasing the number of nearly zero energy buildings. The existing commercial building stock needs to be included in order to achieve the 2020 EU environmental targets. The main barriers of zero energy refurbishment of existing nonresidential buildings appear to be financial rather than technical, next to a number of other extrinsic factors that do not stimulate such an investment. While a business case for new zero energy buildings is believed to exist, controversial opinions can be found with respect to refurbishment of large buildings. The present study aims to identify the factors that affect the feasibility of the zero energy refurbishment of existing commercial buildings, while suggesting ways to create the business case addressing the Dutch market. Through interviews with real estate investors, the study identified the financial and technical barriers encountered today to undertake deep energy retrofit. Subsequently, the design interventions needed to refurbish a Dutch office building and meeting the net zero energy target were evaluated using a software complying with the Dutch standards NEN 7120. A risk and sensitivity analysis with Monte Carlo simulations showed the influence that design aspects, energy price and landlord-tenant agreements have on the business case. The study has concluded that a business case considering the energy savings alone is not sufficient to convince investors. However, when the design provides additional benefits, such as increasing the property value, the refurbishment can become feasible. This is an important observation to promote the refurbishment towards a zero energy building stock.Concrete is, after water, the most used material worldwide and its demand is projected to growth in the next 30 years. Among all concrete materials, cement presents the higher energy consumption and carbon emissions, thats why this industry has been developing several alternatives to gain sustainability. Reduction of clinker ratio by using Supplementary Cementicious Materials (SCM) allows a better use of existing capacities with low investment while a reduction in emissions, costs and energy per ton of cement is observed. The objective of this article is to assess the environmental and economic impact of a new cement with 50% of clinker: Low carbon cement (LC3). A procedure for evaluating sustainable and economic contribution of LC3, while projected demand is satisfied, is designed and applied in several scenarios. The results demonstrate that LC3 introduction is the best option to meet growing demand considering capital investment options in non-developed countries conditions with a reduction of ~30% in carbon emissions, of ~10% in costs and a faster return on investment related to OPC figures in Cuba.