International Concrete Abstracts Portal

This article introduces the latest fiber-reinforced polymer panel system developed by the author—SPiRe®+. These panels can serve as formwork, corrosion resistant reinforcement, and waterproofing. With their flat and smooth exterior face and protruding T-profiles on the interior face, the panels act as reinforcing elements for strengthening beams, slabs, and walls.

While completing concrete repairs, is it necessary to remove sound concrete if a nearby reinforcing bar exhibits rust? Can terms like corrosion or rust be used interchangeably? This month’s Q&A provides answers to these questions as well as a discussion on various factors influencing the extent of a repair of corrosion-related damage in concrete structures.

Developed 40 years ago by Frank Vecchio and Michael Collins, the Modified Compression Field Theory (MCFT) and its successor, the Disturbed Stress Field Model (DSFM), have proven to be robust methodologies in modeling the response of concrete structures. Originally developed for newly designed concrete structures, they have been refined over the years to expand their applicability to various engineering problems, including modeling deteriorated and repaired structures. This paper reviews the evolution and application of MCFT in modeling and assessment of deteriorated and repaired concrete structures. The first part focuses on the application of MCFT to advanced field structural assessment, including stochastic analysis procedures that incorporate field data. The second part discusses the evolvement of MCFT to account for two of the most common deterioration mechanisms, reinforcement corrosion and alkali-silica reaction. The last part explores the application of the model to structures repaired with fiber-reinforced polymer composites. It is concluded that the extension of the MCFT formulation has enabled it to reliably predict the behavior of both deteriorated and repaired concrete structures.

This theoretical study discusses the serviceability of reinforced concrete beams retrofitted with near-surface-mounted (NSM) carbon fiber reinforced polymer (CFRP) strips. Particularly, the research aims to understand the tension stiffening of the strengthened beams under varying degrees of steel corrosion. Five beams are modeled and analyzed, which represent different levels of deterioration up to 100 years. The effects of tension stiffening are evaluated at service and yield loads. Results show that the tension stiffening of the beams decreases as the cross-sectional area of the steel reinforcement reduces. Likewise, the yield and ultimate capacities of the beams diminish with the reduced steel reinforcement. The effective moment of inertia formula stipulated in ACI 318-19 appears to be applicable to the NSM CFRP-retrofitted beams.

The presence of chloride ions is one of the most widespread causes of corrosion initiation in reinforcing steel in concrete. Trace chlorides present in cementitious materials or admixtures typically result in very low fresh chloride contents in normal-strength concrete that do not present a danger of corrosion. UHPC mixture designs, however, use much higher dosages of cementitious materials and admixtures that can result in non-negligible total fresh chloride contents. These high chloride values are likely to occur more frequently in the future as more UHPC mixtures are made with locally available materials and alternative cementitious materials and may result in concrete mixtures failing to meet specifications for fresh chloride content limits that are based on mixture proportions used in normal-strength concrete mixtures. UHPC and normal concrete samples were made without fibers and with increasing levels of internally admixed chlorides for four different levels of strength to determine chloride thresholds for internally added chlorides. The chloride threshold for fresh concrete was measured using a slightly modified version of the accelerated test EN 480-14. The water-soluble and acid-soluble chloride ion content of UHPC mixtures tested were measured according to ASTM C1218 and Florida Method FM 5-516 to determine the bound chlorides and fresh chloride limits for corrosion. The results demonstrate that the UHPC had ~ 25% higher chloride threshold than the control mixture when measured as an absolute content per unit volume of concrete. When the UHPC chloride content is normalized by mass of cementitious material, it was found that the amount needed to initiate corrosion may be lower than fresh chloride limits given in ACI-318 and ACI 222. Therefore, the ACI-318 water-soluble chloride limits as a % by mass of cementitious materials were found to be non-conservative for the two of the UHPC mixtures tested and should be re-examined for UHPC.