Comparison of Destructive Methods to Appraise the Mechanical Integrity of a Concrete Surface

peer reviewedDepending on the technique being used, the concrete removal operation prior to repair can be harmful to the residual concrete skin left on the structure. Whenever a tight bond between the repair and the old concrete is required, the soundness of the prepared surface should thus be assessed. Although this is widely recognized, there is no standard method intended to characterize the integrity of a concrete substrate after concrete removal. This paper presents the results of an investigation intended to assess and compare quantitatively different test methods, namely the Schmidt rebound hammer, the pull-out test and the pull-off test, to evaluate superficial mechanical integrity of a substrate after concrete removal operations. Although it does not yield a precise evaluation of compressive strength, the Schmidt rebound hammer test is recognized as a useful tool for performing quick surveys to assess concrete uniformity. The pull-off test is very well correlated with the splitting-tensile test, but it is not suited for vertical and overhead surfaces. The Capo pull-out test has limited interest for surface preparation, as it is applicable to flat surfaces only. Conversely, the accelerated pull-out test showed interesting potential as a simple and relatively rapid means for assessing the mechanical integrity of a concrete surface prior to repair for any type of concrete surface. More work is definitely required to refine the procedures and develop performance criteria. Nevertheless, it appears from the results generated in this study that the combination Schmidt hammer / pull-off test could fill the needs for the evaluation of horizontal surfaces after concrete removal, while the combination Schmidt hammer / accelerated pull-out test could be used effectively on vertical and overhead surfaces.Coopération scientifique WBI/Québe

Concrete repair bond: evaluation and factors of influence

peer reviewedRepair and strengthening of existing concrete structures are among the biggest challenges civil engineers are facing today and will have to face in the years to come. Present concerns of sustainable development emphasizing repair instead of new construction will only strengthen this trend. Concerted efforts towards improving the durability of concrete repairs are still needed from scientists and engineers. One of the critical aspects of durability of concrete repairs and overlays is lasting and sufficient interfacial bond between repair material and existing concrete substrate. This paper summarizes some of the findings of a collaborative study devoted to the most significant factors influencing bond in repairs (roughness, degree of saturation and carbonation of the substrate) and its field evaluation (type of loading, device misalignment). Based on the test results collected in different test programs, guideline-type recommendations for surface preparation prior to repair were issued

Cellular IP₆ Levels Limit HIV Production while Viruses that Cannot Efficiently Package IP₆ Are Attenuated for Infection and Replication

Summary: HIV-1 hijacks host proteins to promote infection. Here we show that HIV is also dependent upon the host metabolite inositol hexakisphosphate (IP6) for viral production and primary cell replication. HIV-1 recruits IP6 into virions using two lysine rings in its immature hexamers. Mutation of either ring inhibits IP6 packaging and reduces viral production. Loss of IP6 also results in virions with highly unstable capsids, leading to a profound loss of reverse transcription and cell infection. Replacement of one ring with a hydrophobic isoleucine core restores viral production, but IP6 incorporation and infection remain impaired, consistent with an independent role for IP6 in stable capsid assembly. Genetic knockout of biosynthetic kinases IPMK and IPPK reveals that cellular IP6 availability limits the production of diverse lentiviruses, but in the absence of IP6, HIV-1 packages IP5 without loss of infectivity. Together, these data suggest that IP6 is a critical cofactor for HIV-1 replication

Evaluation of the mechanical integrity of a concrete surface by means of combined destructive methods

peer reviewedAs a tight bond between the repair and the old concrete is required, the soundness of the prepared surface has to be carefully assessed. This paper presents the results of an investigation intended to assess and compare quantitatively different test methods, namely the Schmidt rebound hammer, the pull-out test and the pull-off test, to evaluate superficial mechanical integrity of a substrate after concrete removal operations. Although it does not yield a precise evaluation of compressive strength, the Schmidt rebound hammer test is recognized as a useful tool for performing quick surveys to assess concrete uniformity. The pull-off test is very well correlated with the splitting-tensile test, but it is not suited for vertical and overhead surfaces. The Capo pull-out test has limited interest for surface preparation, as it is applicable to flat surfaces only. Conversely, the accelerated pull-out test showed interesting potential as a simple and relatively rapid means for assessing the mechanical integrity of a concrete surface prior to repair for any type of concrete surface. It appears from the results generated in this study that the combination Schmidt hammer / pull-off test could fill the needs for the evaluation of horizontal surfaces after concrete removal, while the combination Schmidt hammer / accelerated pull-out test could be used effectively on vertical and overhead surfaces

Specifying Concrete Repair Materials

peer reviewedSpecification of materials for concrete repair is a complex task requiring broad knowledge of materials science, engineering and construction practice. In this paper, several issues important for proper design and implementation of concrete repair are discussed. It is stressed that the specification documentation is not a formality, but rather a critically important engineering step in view of fulfilling the durability and service life requirements

Repairing Concrete Industrial Floors with Bonded Cement-based Material Overlays: some recommendations

peer reviewedSince concrete has been used for more than a century, many structures need repair in different degrees and others need strengthening to withstand higher loads. Moreover, the number of new concrete structures is constantly increasing, and therefore repair or retrofitting requirements increase. Present concerns of sustainable development emphasizing repair or strengthening instead of new construction, acts as incentive to this trend. The bonded overlay technique is particularly suitable in the case of structures with large areas like industrial floors. This paper has the ambition to present reliable design methodology for the practitioner. Surface preparation, overlay design and material selection, application process and QC/QA are discussed and guidelines are proposed in order to enhance quality of repair operations

A quantitative approach to the concept of concrete repair compatibility

peer reviewedThe work reported in this paper is part of a wider research program intended to provide the repair industry with improved fundamental knowledge to implement rational design methods and rules for repairs. In that regard, there is a strong need to study the fundamental relationships and parameters that underlie the repair compatibility concepts, in particular those relating to dimensional compatibility. In the first part of the paper, classical formulas derived for thick cylindrical specimens were used to analyze the tensile stress buildup in annular restrained shrinkage test specimens, taking into account the restraining conditions the investigated ring test method and the individual concrete properties/phenomena determined experimentally (elastic modulus, creep coefficient, drying shrinkage deformation). By comparing the ring test results with the calculated tensile stresses, the validity and accuracy of the theoretical approach could be appraised. A quantitative approach for the evaluation of the performance of concrete repair in terms of dimensional compatibility was then developed. Derived from the basic strain balance approach (ratio between the total deformability in tension and the drying shrinkage deformation), a parameter referred to as dimensional compatibility index (CI) was introduced in order to analyze the evolution of dimensional compatibility as a function of time for a given concrete mixture, taking into account the actual degree of restraint in the element. Compatibility index evolution curves were calculated for various repair concrete mixtures in order to highlight material behavior relating to composition parameters and temperature. As it requires the evaluation of a limited number of individual properties that are for most readily available (i.e. strength, elastic modulus, shrinkage), the compatibility index expressed in terms of deformation carries a lot of potential as a relatively simple and convenient analytical tool for assessing the cracking sensitivity of concrete repair materials. Overall, it can be stated that a good correlation was found between the ring test results and the tensile stress values calculated based on individual concrete properties / phenomena and that the proposed calculation method lays ground for evaluating quantitatively the dimensional compatibility of repair materials and defining suitable performance criteria

Recommandations pour la réparation, le re-surfaçage ou le renforcement des dallages industriels ou des chaussées en béton par un rechargement adhérent à base cimentaire

The recommendations presented in this publication are inspired by the State of the Art Report edited by the RILEM technical committee TC 193 RLS Bonded cement-based material overlays for the repair, the lining or the strengthening of slabs and pavements. The objective is to lay out all the practical aspects to be considered in the design of concrete overlays: bonded concrete overlay process, assessment of the existing structure, surface preparation, overlay materials, design methods, construction procedure and quality control/assurance (QC/QA) system, and maintenance

Development of Specifications and Performance Criteria for Surface Preparation Based on Issues Related to Bond Strength

In addition to the development of a satisfactory test procedure and recommendations to improve the overall quality of concrete repair works, the authors of this proposal intend to collaborate with various representatives from public agencies and from the industry to facilitate technological transfer. Presentations will be made in conferences and workshops in North America and Europe. At the end of the project, the results shall include two MSc theses and at least two papers in major journals, such as Concrete International or ACI Materials Journal. Also, the project should provide the basis towards a standard procedure for the evaluation of superficial cohesion of concrete, in relation with surface preparation and concrete removal techniques. Finally, recommendations and specifications could be incorporated in future versions of the ACI-ICRI Manual of Concrete Repairs as well as in DOT’s specifications

Évaluation des réparations en béton et identification des principaux facteurs d’influence

peer reviewedLa réparation et le renforcement des structures existantes en béton comptent parmi les plus importants défis auxquels les ingénieurs civils sont confrontés aujourd’hui et qu’ils devront relever dans les années à venir. Les préoccupations actuelles concernant le développement durable favorisent la réfection au détriment de la construction neuve et ne peuvent que renforcer cette tendance. Des efforts concertés de la part des scientifiques et ingénieurs sont encore nécessaires afin d’améliorer la conception des réparations en béton et d’en assurer la qualité et la fiabilité attendues. L’un des aspects essentiels de la durabilité des réparations en béton et des revêtements ou traitements de surface est la qualité de l’adhérence entre le matériau de réparation et le béton existant. Le présent article résume les principales conclusions de travaux réalisés en collaboration en vue d’identifier les facteurs influençant l’adhérence des réparations (la rugosité, le degré de saturation et la carbonatation du substrat) et l’évaluation de celle-ci en conditions in situ (type de chargement, alignement de l’appareil). Sur la base des résultats recueillis, des recommandations ont été émises dans un guide du USBRCoopération scientifique avec le Québec et la Pologn