International Concrete Abstracts Portal

SYNOPSIS: The use of wet lay-up fiber-reinforced polymers (FRPs) in the construction industry continues to grow. Their lightweight, durability, and good material properties makes them very desirable in the concrete repair industry. Research has shown that these products greatly improve the strength of repaired corroded members and reduce the rate of post-repair corrosion. There is a lack of research, however, in understanding how curing of these systems in the presence of moisture or underwater may affect their ability to strengthen and protect reinforced concrete. In this paper, data on material properties of a prepreg system, cured in laboratory conditions and under-water is presented and compared. The results show that there is a very small drop in tensile material properties when the system is cured underwater. Compression of concrete cylinders strengthened with one layer of the system and cured underwater is shown to be in agreement with ACI 440.2R-08’s confinement equations. Durability testing of the bond between the system and reinforced concrete using dolly pull-off test shows a 90% bond strength retention after 1,000hr exposure to various aggressive environments.

Since the late 1980s, FRP products have seen increased use in repair and strengthening of concrete structures. The traditional technique is referred to as wet layup where carbon or glass fabric are saturated with epoxy in the field and applied to the structure. In this paper I present several new products that I have developed in recent years. One is very large pre-cured carbon or glass laminate sheets that can be used to repair columns, piles underwater, pipelines, etc. The other is a honeycomb-FRP combination that allows construction of lightweight stiff elements. This product can be used to build pipes that can serve as free-standing elements or in slip-lining repair of deteriorated culverts and pipes. These products can also be used as stay-in-place forms for repair of seawalls, large piers and the like. Examples of field applications are also presented.

The poor performance of conventional chip and patch methods for repairing corrosion damaged piles has led to renewed interest in the use of fiber reinforced polymers (FRP). Over the past decade, laboratory research complemented by numerous field demonstration projects has led to improvements in the design, construction and monitoring of FRP pile repair. The two principal areas of advancement were in the development of techniques borrowed from the composites industry for improving FRP-concrete bond and in the incorporation of a sacrificial anode cathodic protection system within a FRP wrap. Both developments enhance the competitiveness of FRP pile repair. This paper provides an overview of laboratory and field demonstration studies in recent years that led to these advancements.

Viscosity-enhancing agents (VEA) are often used to improve the cohesiveness and stability of self-consolidating and underwater concrete. However, because of various types of interactions occurring between the VEA polymers and other components of fresh cementitious systems, the beneficial effects of the VEA is found to depend on the nature of both the VEA and the other the other components, particularly the superplasticizer (SP). Hence, different VEA-SP combinations are found to yield different dose-response effects in application. To investigate the origin and consequences of VEA-SP interactions, the influence of two common VEAs on the properties of cementitious and reference (limestone) systems was investigated through rheological and stability (bleeding and segregation) measurements in the presence of two typical SPs, a naphthalene-based (PNS) and a carboxylate-based (PC) polymer. The rheology of cement and powdered limestone pastes was evaluated through the Kantro mini-slump test and from measurements of yield stress and plastic viscosity in simple shear, and dynamic moduli obtained through oscillatory measurements. The bleeding and sedimentation behaviors were monitored using a multipoint conductivity method. Corresponding rheology and stability data were also obtained on mortars incorporating the same VEA-SP admixture combinations. In these systems, the different VEA-SP couples demonstrate varying compatibility which impact on their performance.

Nano-technology based on depth-sensing microindentation apparatus was used to evaluate the elastic modulus and micro-hardness of the interfacial transition zone (ITZ) and to estimate the extent of the ITZ around the aggregate-matrix interface for underwater concrete (UWC) and around steel reinforcement for selfconsolidating concrete (SCC) and vibrated concrete. The micromechanical properties of ITZ near to aggregates of concrete cast in water were lower than those of concrete cast in air. The modulus elasticity and the microstrength of concrete cast in water were lower than those of concrete cast in air. It is attributed to the dilution of paste cement and fines particles in water causing reduction of strength and increasing the porosity of concrete. The results of the interfacial properties between selfconsolidating concrete and conventional concrete revealed that the elastic modulus and the micro-strength of the ITZ were lower on the bottom side of a horizontal steel bar than on the top side, particularly for the vibrated reference concrete. The difference of ITZ properties between top and bottom side of the horizontal steel bar appeared to be less pronounced for the SCC mixtures than for the corresponding control mixtures.