International Concrete Abstracts Portal

A novel self-healing system for cement composites is proposed in this study. It is based on the use of extruded cementitious hollow tubes filled with a liquid healing agent to be added in cement composites during mixing. These tubular capsules were characterized in terms of flexural strength, liquid storage capability, mixing survival effectiveness and releasing ability upon crack formation. The suitability of a specific mono-component liquid healing agent – a sodium silicate solution – was also assessed. Finally, the self-healing effectiveness of the proposed system was verified using a three-point-bending procedure to induce crack formation on laboratory scale specimens and to evaluate their mechanical recovery after self-healing. Positive results were achieved, though further research is needed to reach a final optimization.

Simply-supported one-way R/C slabs are commonly used in the covers of small and medium underground facilities, where durability is the main issue face with rather limited service loads and short spans (2-4 m [6.5-13.0 ft]). The structural performance, however, should not be underrated, as being the slab in a roundabout does not prevent a heavy truck from straying off the right lane! To have fresh information on durability and cracking (working loads), and on the bearing capacity and failure mode (ultimate loads), displacement-controlled tests have been recently performed in Milan on four typical rectangular R/C slabs suspended along their short sides via corbels (dapped ends; size: 1.3x2.2x0.15 m [51x87x6 in.]). A transversely-distributed or concentrated load was applied either at mid-span (in the bending tests), or at 1/10 of the span (in the shear tests). The two slabs Type A are provided with longitudinal bent-up bars in the main body and hooks in the corbels. On the contrary, the slabs type B are reinforced via two continuous layers of longitudinal straight bars. Under the working loads, cracking never occurred, neither in bending nor in shear – to the advantage of durability – while above the working loads rather complex crack patterns formed in the D zones close to the corbels, particularly under the concentrated load, which brought in 3-D effects, with a limited reduction in the bearing capacity. Refining the reinforcement layout is shown – once more - to markedly improve slab performance, with little or no extra cost.

Editors: Mario Alberto Chiorino, Luigi Coppola, Claudio Mazzotti, Roberto Realfonzo, Paolo Riva

With the dawn of twenty-first century, the world has entered into an era of sustainable development. The main challenge for concrete industry is to serve the two major needs of human society, the protection of the environment, on one hand, and - on the other hand - meeting the infrastructural requirements of the world growing population as a consequence of increase in both industrialization and urbanization. In the past, concrete industry has satisfied these needs well. Concrete is an environmentally friendly material useful for the construction of vast infrastructures. Skyscrapers, highway bridges, roads, water retaining structures and residential buildings are all testimonials to concrete’s use and versatility. However, for a variety of reasons the situation has changed dramatically in the last years. First of all, the concrete industry is the largest consumer of natural resources. Secondly, portland cement, the binder of modern concrete mixtures, is not as environmentally friendly. The world’s portland cement production, in fact, contributes to the earth’s atmosphere about 7% of the total CO2 emissions, CO2 being one of the primary greenhouse gases responsible for global warming and climate change. As a consequence, concrete industry in the future has to face two antithetically needs. In other words how the concrete industry can feed the growing population needs being – at the same time - sustainable?

ACI Italy Chapter has been playing a significant role in the last years in the broad area of concrete technology in Italy and, in particular, in the field of concrete durability and sustainability. ACI Italy Chapter has become increasingly involved in research and development dealing with durability and sustainability issues such as reduction in CO2 emissions, use of recycled materials and innovative products, design of durable structures and maintenance, repair and refurbishment of concrete infrastructures.

In October 2015, the American Concrete Institute Italy Chapter (ACI IC) and the Department of Civil, Chemical, Environmental, and Material Engineering (DICAM) of the University of Bologna sponsored the First International Workshop on “Durability & Sustainability of Concrete Structures” in Bologna (Italy). The workshop was co-sponsored by the American Concrete Institute and ACI Committee 201. The proceedings of the workshop were published by ACI IC as SP305. The proceedings consist of forty-eight refereed papers concerning reduction in green house gases in cement and concrete industry, recycled materials, innovative binders and geopolymers, Life Cycle Cost Assessment in concrete construction, reuse and functional resilience of reinforced concrete structures, repair and maintenance, testing, inspection and monitoring.

Many thanks are extended to the members of the technical paper review panel. Without their dedicated efforts it would not have been possible to publish the proceedings. The cooperation of the authors in accepting reviewers’ comments and suggestions and in revising the manuscripts accordingly is greatly appreciated.

Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-305

Advances in concrete technology have led to a widespread use of High Performance Concretes (HPC) with a low water/binder ratio. Those concretes are prone to early age cracking because of the increased autogenous shrinkage, which is normally insignificant for w/b greater than 0.4 and appears mostly in the first days after setting, when the concrete has not reached its full tensile strength, and so it’s one of the principal causes of early age cracking impairing the structure durability. This study aims at quantifying the efficiency of Internal Curing with pre-saturated Light Weight Aggregates (LWA) on the reduction of autogenous shrinkage in HPC. A standard mixture (w/c = 0.3) was tested together with an Internal Cured one, in which a fraction of the normal weight aggregate was replaced by a pre-wetted LWA, to evaluate the differences in the mechanical properties (compressive and tensile strength, elastic modulus) and shrinkage behavior (plastic, autogenous, drying free and restrained shrinkage). In face of a slight decrease of the strength (about 9%) which did not compromise the structural use of the concrete, the pre-wetted LWA led to a 30% decrease of autogenous shrinkage, and a roughly 50% reduction in cracking potential.

Self-healing cementitious composites are a broad category of smart construction materials to which strong and highly qualified research efforts are currently being devoted worldwide, with the aim of providing a sound scientific background to their consistent, and – design-wise – “consciously safe”, use in the engineering practice. Tailored additions can be employed to enhance the self-healing capacity, among which the so-called crystalline admixtures, play a prominent role. Crystalline admixtures consist of proprietary active chemicals, which, because of their hydrophilic nature, react with water and cement particles in the concrete to form calcium silicate hydrates, increasing the density of the CSH phase, and/or pore-blocking precipitates in the existing micro-cracks. The mechanism is analogous to the formation of CSH and the resulting crystalline deposits become integrally bound with the hydrated cement paste, thus contributing not only to a significantly increased resistance to water penetration but also to the healing of the existing damages and cracks. This paper summarizes the results of a wide experimental investigation jointly performed by Politecnico di Milano (Italy), Indian Institute of Technology Madras, Chennai (India) and Universitat Politecnica de Valencia (Spain) to assess the effectiveness of different commercially available crystalline admixtures on the self-healing capacity of cement based materials.