Patch repair: compatibility issues

peer reviewedRepair of any concrete structure results in formation of complex, at least two-component repair systems. Compatibility approach is treated as a basic requirement during selection of repair material. Recently, the understanding for compatibility requirements in repair systems approach is demonstrated in many papers. The aim of this paper is analyzing the compatibility between repair materials and concrete substrate in the case of patch repair. The compatibility issues were discussed in light of the various requirements which determine the mathematical space of loads, including chemical, mechanical and other physical (mainly thermal) loads. N-dimensional compatibility space is created, taking into account selected patch material control parameters. The requirements for good compatibility between repair material and concrete substrate can be formulated by using mathematical inequalities, where the variables are the material control parameters. The effects of properties of the both repair material and concrete substrate were analyzed using computer system ANCOMP developed at Warsaw University of Technology. Usability of this approach was demonstrated using selected case study as an example

Study of bond between epoxy, steel reinforcing bars and concrete affected by alkali-silica reaction

Installation of drilled-in epoxy bonded reinforcing barsis generally an effective strengthening method for deficient concretestructures. However, this method of rehabilitation has largely been studied and tested on sound concrete elements, i.e. without any pathological damage, which raisesthe question of bond capabilities inexisting damaged elements. This investigation studies the influence of alkali-silica reaction (ASR) onthe capacity of epoxy bonded anchors. ASR, which is very common in eastern Canada, results from the chemical reaction between the alkali hydroxides in the concrete’s pore solution and some siliceous mineral phases inthe aggregates. Pull-out tests on epoxy bonded anchors havingembedded lengths offourtimes the bar diameter(Ø= 16 mm)have demonstrated a drop in bond strength when concrete is affected by ASR. In addition, the study revealed that the progression of concrete expansion due to ASR, leads to a confinement of the epoxy bonded anchor and increases the bond strength. These conclusions are therefore considered for the development of a model for the design of epoxy bonded anchors in existing concrete infrastructure affected by ASR

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

The effect of wood ash as a partial cement replacement material for making wood-cement panels

The aim of this study was to consider the use of biomass wood ash as a partial replacement for cement material in wood-cement particleboards. Wood-cement-ash particleboards (WCAP) were made with 10%, 20%, 30%, 40%, and 50% of wood ash as a partial replacement for cement with wood particles and tested for bending strength, stiffness, water absorption, and thermal properties. Test results indicate that water demand increases as the ash content increases, and the mechanical properties decrease slightly with an increase of the ash content until 30% of replacement. On the other hand, the heat capacity increases with the wood ash content. The WCAP can contribute to reducing the heat loss rate of building walls given their relatively low thermal conductivity compared to gypsum boards. The replacement of cement to the extent of approximately 30% by weight was found to give the optimum results

UNDERSTANDING THE PUMPABILITY OF CONCRETE

With the increasing need for underground opening\u27s support and the increasing knowledge available today in concrete technology, shotcreting, and particularly the wet-mix process, is in great demand. Successful pumping operations however usually require a certain amount of experience. On the one hand, engineers design a mixture with high workability for ease of transport through the hose system, and on the other hand, they strive for a mixture that is relatively stiff, adhesive, and cohesive to achieve good adhesion and build-up on vertical or overhead shooting surfaces. This article presents some of the most recent research on the understanding of the key parameters affecting concrete mobility and stability under pressure, i.e. pumpability. Taking into account the mechanics of full size pumping equipment, the concept of Real Paste Content is introduced as a minimal quantity of effective paste under pressure available for mobility through a hose system. Experimental results used to validate the concept allow explanation of behavioral variations between the different concrete mixtures

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

Reinforced concrete repair - Part 1 : Pathologies et diagnosis

peer reviewedLa réparation des bétons nécessite non seulement une bonne connaissance du support à réparer, des matériaux de réparation et de l’environnement dans lequel ils vont être mis en œuvre, mais aussi une compréhension des mécanismes à la base de l’adhésion. Les compatibilités dimensionnelle, électrochimique, chimique et porosimétrique (perméabilité) sont les clés de la réussite et de la durabilité de la réparation. Dans cette première partie, une analyse du patrimoine bâti en jeu et des stratégies d’intervention possibles est d’abord proposée. L’accent est mis ici sur l’étude des effets et des causes des dégradations affectant les ouvrages en béton armé: fissuration, épaufrures et désintégrations sont les principaux types de défauts de surface observés, en lien très souvent avec la corrosion des armatures en acier sous-jacentes. Un diagnostic juste permettra de définir les techniques d’intervention et les produits de réparation les mieux adaptés (Partie 2).Repair of concrete not only requires knowledge of the support to repair, the repair materials and the environmental conditions in which they will be implemented, but also an understanding of the mechanisms underlying adhesion. Dimensional, electrochemical, chemical and porosity (permeability) compatibilities are the key to the success and durability of the repair. In a first part, an analysis of the patrimonial heritage at stake and the possible intervention strategies is proposed. The emphasis is put here on the study of the effects and causes of deterioration affecting reinforced concrete structures: cracking, spalling and disintegration are the main types surface defects observed, most often in connection with corrosion of the underlying steel reinforcement. A proper diagnosis will allow selecting the most suitable repair techniques and materials (Part 2)

Reinforced concrete repair - Part 2 : Compatibility and performance

peer reviewedLa réparation des bétons nécessite non seulement une bonne connaissance du support à réparer, des matériaux de réparation et de l’environnement dans lequel ils vont être mis en œuvre, mais aussi une compréhension des mécanismes à la base de l’adhésion. Les compatibilités dimensionnelle, électrochimique, chimique et porosimétrique (perméabilité) sont les clés de la réussite et de la durabilité de la réparation. Sur la base de l’analyse du patrimoine en béton armé et des stratégies d’intervention possible, l’accent a été placé dans la première partie sur l’étude des effets et des causes des principaux défauts de surface observés. Une fois la condition du béton en place adéquatement évaluée (Partie 1), la préparation de la surface avant réparation, sa propreté ou encore sa rugosité sont des conditions essentielles au développement de l’adhérence et de l’accrochage du produit de réparation, garantissant ainsi la durabilité de l’intervention

Compatibility performance as a fundamental requirement for the repair of concrete structures with Self-Compacting Repair Mortars

peer reviewedDurable adhesion of repair material on concrete substrate requires compatibility between the materials to be bonded. There are four main compatibility components to be addressed in any concrete repair scenario: dimensional, permeability, chemical and electrochemical compatibility. Among those, dimensional compatibility is often prevalent: while a cement-base repair material inevitably undergoes shrinkage, the substrate opposes to its free movement, a situation that can lead to cracking and, subsequently, promote debonding. Besides, an essential requirement for bond development is the creation of the interface itself: the intimate contact between the repair system and concrete substrate is required in order to maximize adhesion. Adequate compaction of the new layer is consequently one of the main parameters that will govern the quality of the bond: sufficient vibration or specific rheological properties for the repair material are needed. Self-Compacting Repair Mortar (SCRM) can be advantageously used in many repair situations. Limestone fillers seem to offer interesting advantages as addition to these repair materials as they increase the workability of the final product. Several materials have been tested and characterised by means of a physical, chemical and mechanical characterization test program: specific attention has been given to water demand and superplasticizer efficiency