International Concrete Abstracts Portal

This paper presents a robust mathematical model to predict the long-term behavior of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) sheets. The model is constructed using the theory of Polynomial Chaos Expansion (PCE) in conjunction with the adjusted effective modulus method. The formulation of PCE is composed of quadrature rules, variable transformations, and solution algorithms, including a step-by-step implementation procedure. After verifying the modeling approach against experimental beams taken from literature, a benchmark beam is designed and used for parametric investigations in order to understand the effects of various attributes on the strengthened beam subjected to sustained loads for up to 4000 days. The creep and shrinkage of the concrete appreciably develop with time, whereas the macroscopic behavior of CFRP is relatively insusceptible. The sectional response of the beam alters owing to the increased concrete strain and stabilizes as the amount of compression steel rises. The debonding failure of CFRP is not noticed when the beam is loaded up to 50% of its flexural capacity. The efficacy of CFRP-strengthening is substantiated through reducing steel stresses and long-term deflections, which are particularly noticeable when the beam cracks.

Cracks in bridge decks facilitate the penetration of chlorides that induce corrosion of reinforcing steel. Formation of cracks is related to the shrinkage and properties of the concrete and the restraints to movement. Lightweight concrete with a low modulus of elasticity, high creep, and water in the aggregate pores for internal curing has a reduced cracking potential. To control cracking, shrinkage of concrete can be reduced by using a shrinkage-reducing admixture (SRA). A recent study at the Virginia Department of Transportation (VDOT) investigated the performance of both lightweight concretes and concretes with SRA containing normal-weight aggregates in the field and found that these concretes had no cracks or fewer cracks than were typical of decks constructed with normal-weight aggregates over the past 20 years. VDOT developed a new specification that included lightweight concretes or concretes with normal-weight aggregates and SRA and this specification is being used successfully to reduce cracking in bridge decks. This paper summarizes the work conducted to develop the new specification and includes information on field applications.

The presence of uncontrolled or unexpected nonstructural cracking in reinforced concrete structures generally leads to conflict and disputes. The current industry practice aims to prevent or mitigate the presence of cracking at early ages (that is, plastic shrinkage, thermally induced cracking) or due to volumetric changes (restrained or drying shrinkage). However, cracking of concrete can still occur and lead to questioning the durability of concrete with prolonged service life expectations such as bridge decks, piers, or waterfront structures, to name a few. The effect of cracks on chloride penetration has been thoroughly studied, and evidence of the effect of cracks on accelerated ingress of chlorides is well established. Structural codes and guides, on the other hand, consider that the integrity of the concrete element is not significantly affected as long as the crack width does not exceed a recommended limit based on exposure conditions. Similarly, service life predictions based on chloride ingress modeling disregard the effect of cracks. Because crack-free concrete cannot be guaranteed, service life predictions that neglect the effect of cracks can be significantly inaccurate. A simplified approach is presented in this paper, where a correction to the chloride diffusion coefficient of concrete is performed to account for the effect of cracks. This correction is similar, in principle, to the so-called aging or decay coefficient in concrete. Results of Monte Carlo simulations on chloride ingress and estimations of the time-to-corrosion initiation are presented and discussed. Results indicate that a decrease of the reliability index (β), or an increase in the probability of failure (pf), can be calculated when accounting for the effect of cracks.

This paper presents a new concept of high-performance structures composed of internally cured concrete and glass fiber-reinforced polymer (GFRP) reinforcement. The former addresses autogenous shrinkage that leads to premature cracking of concrete, and the latter provides a noncorrosive service environment. Presaturated superabsorbent polymer (SAP) is mixed with concrete at 0 to 0.4% of the cement mass to facilitate a hydration process. The swelling kinetics of SAP due to water absorption is quantified, and its releasing rate with time is determined. A total of 15 one-way slabs are tested in flexure to examine the effects of SAP inclusions. The behavior of the slabs is assessed by deterministic and stochastic models with an emphasis on tension stiffening and performance reliability. The amount of the internal curing agent affects the strength of the concrete and the response of the slabs. Various cracks are observed when the slabs are loaded, including flexural, horizontal splitting, and diagonal tension cracks. As the amount of SAP increases, the cracks become localized and expedite the failure of the slabs. The tension stiffening of control slabs (0%SAP) is more pronounced than that of the slabs with SAP. The cumulative degradation probability and the risk level of the slabs made of the internally cured concrete are controlled by the amount of SAP.

This paper presents a real case study concerning the analysis of the cracking risk of a large reinforced concrete slab-on-ground with 9.84 in. (250 mm) of thickness and approximately 9257 ft2 (860 m2) of area. It was designed to prevent effects of severe environment conditions over the life span as thermal and drying shrinkage. This slab is a pool floor without expansion joint—jointless—to avoid leakage and early deterioration of the structure. The main properties were initially estimated based on the thermal structure behavior to evaluate the volume change effect from early ages to long-term effects. The proposed solutions to reduce the volume change effects of concrete were carried out in three parts: improvements in structural design; optimization of the concrete mixture; and adjustments in the construction process. After the concrete placement, the solutions proved to satisfactorily prevent cracks, thus ensuring proper performance of the pool.