Allan Scott

Performance of Slag Concrete in Marine Environment

The authors report on concrete incorporating ground pelletized blast-furnace slag evaluation findings after being exposed to a marine tidal zone environment for 25 years. In order for laboratory evaluation to occur, two large concrete blocks (305 x 305 x 915 mm [1 x 1 x 3 ft]) were sampled after being retrieved from the exposure site. Three series of mixtures with 0.40, 0.50, and 0.60 water-cementitious material ratios (w/cm) supplied the specimens; concrete mixtures within each series contained 0, 25, 45, or 65% slag by total cementitious materials mass. For concretes containing higher levels of slag (45 or 65%) with a w/cm or 0.50 or 0.60, there was observation of severe surface erosion, increasing slag levels correlating with increasing levels of damage. For all concretes with a 0.40 w/cm, however, the surface condition was satisfactory. Determination of chloride ion penetration depth, hardened air-void parameters, chloride diffusion, chloride permeability (ASTM C1202) splitting strength, modulus of elasticity, and compressive strength were included in laboratory testing. After 25 years of exposure, chloride penetration depth for all control concretes (i.e., without slag) was greater than 100 mm (4 in.) regardless of the w/cm. Significantly greater chloride ion penetration resistance (generally <50 mm [2 in.] for 45 and 65% slag) was shown by slag concretes, with penetration depth decreasing with decreasing w/cm and increasing slag content. In terms of mass transportation reduction, laboratory tests confirmed slags beneficial effect with more than tenfold reductions in chloride permeability and diffusion coefficients shown by the slag concretes. That slag use, provided the w/cm is kept low (i.e., w/m is less than or equal to 0.40), at relatively high replacement levels by North American standards (i.e., 45 to 65%) results in a significant concrete performance increase in a very aggressive marine environment is indicated by the data.

Complete Model of Corrosion-Degraded Cyclic Bond Performance in Reinforced Concrete

AbstractThis paper investigates the effects of deterioration due to corrosion on monotonic and cyclic bond performance. Forty-two monotonic and cyclic pullout tests were undertaken on well-confined corroded reinforced concrete specimens, with corrosion levels ranging from 0 to 25% reinforcement mass loss. Experimental results were used in the development of a corrosion-dependent cyclic bond-slip model that recreates the effects of corrosion on reinforcement bond. The model allows for alteration of the monotonic pullout curve along with altered damage relationships under cyclic loading to account for corrosion of reinforcement. Impressed current techniques were used to achieve the desired level of corrosion, and the results of this research provide a term of comparison for future studies on specimens subject to natural corrosion processes.

Seismic Performance of High-Strength Self-Compacting Concrete in Reinforced Concrete Beam-Column Joints

AbstractBecause of its potentially beneficial properties, there has been an increased interest in recent years on performance of self-compacting concrete (SCC) in structural members. The capability of SCC in flowing through and filling in even the most congested areas makes it ideal for use in congested reinforced concrete (RC) structural members such as beam-column joints (BCJ). However, members of tall multistory structures impose high capacity requirements where implementing normal-strength self-compacting concrete (NSSCC) is not preferable. In the present study, six beam-column joint specimens were designed following the guidelines of the New Zealand concrete standards; namely, three high-strength self-compacting concrete (HSSCC), one conventionally vibrated high-strength concrete (CVHSC), one conventionally vibrated concrete (CVC), and one CVC with HSSCC in its joint region. Factors such as the concrete type (HSSCC, CVHSC, and CVC), amount of joint shear stirrups, axial load ratio (1% and 10% of sect...

Evaluation of Fly Ash From Co-Combustion of Coal and Petroleum Coke for Use in Concrete

An investigation of fly ash (FA) produced from various blends of coal and petroleum coke (pet coke) fired at Belledune Generating Station, New Brunswick, Canada, was conducted to establish its performance relative to FA derived from coal-only combustion and its compliance with CSA A3000. The FA samples were beneficiated by an electrostatic separation process to produce samples for testing with a range of loss-on-ignition (LOI) values. The results of these studies indicate that the combustion of pet coke results in very little inorganic residue (for example, typically less than 0.5% ash) and the main impact on FA resulting from the co-combustion of coal and up to 25% pet coke is an increase in the unburned carbon content and LOI values. The testing of FA after beneficiation indicates that FA produced from fuels with up to 25% pet coke performs as good as FA produced from the same coal without pet coke.

Seismic Behavior of Corroded RC Bridges: Review and Research Gaps

Chloride-induced corrosion and its effect on structural and seismic performance of reinforced concrete (RC) structures have been the topic of several research projects in past decades. This literature review summarizes the state of the art by presenting a brief description of chloride-induced corrosion, its main characteristics and influencing factors, a summary of experimental published data, and existing corrosion-induced deterioration models together with numerical and experimental methods used to evaluate corroded RC bridge pier. This literature review highlights the need for reliable deterioration models for RC structures and appropriate analysis methods are needed for design of new structures or assessment of existing civil engineering structures especially in seismic areas.

Durability Properties of Sprayed Engineered Cementitious Composite

Engineered cementitious composite (ECC) shotcrete is a sprayable cement composite reinforced with synthetic fibers that exhibits a strain-hardening characteristic under tension. The ductile behavior of ECC makes it an ideal repair material for concrete structures as tensile strains from expansion of the original concrete structure can be accommodated. The aim of the reported research was to develop an ECC mixture design having superior durability properties while exhibiting a strain-hardening characteristic. Six mixture designs of ECC and a 5800 psi (40 MPa) cast-inplace concrete were tested using four test methods to determine their chloride resistance. Results from bulk diffusion testing showed that the most effective ECC mixture design, which incorporated a metallic soap additive, showed a 90% reduction in the chloride diffusion coefficient when compared with a 5800 psi (40 MPa) cast-in-place concrete. The alternating current (AC) resistivity, void, and sorptivity tests conducted did not show a strong correlation to the bulk diffusion test.

Short-term behaviour of reinforced and steel fibre–reinforced concrete composite slabs with steel decking under negative bending moment:

An experimental study was conducted on reinforced and steel fibre–reinforced concrete composite slabs with steel decking under negative bending moment to quantify the ultimate behaviour, loading capacity and crack width under short-term loading. Eight full-scale slab specimens were cast with different types and amounts of reinforcement in the concrete (e.g. mesh, steel fibre or normal reinforcing bars) but with the same type of steel decking. Each slab was simply supported and tested in four-point bending under increasing load until failure. The deflections at mid-span and under the applied point loads were monitored together with the end interface slip. The crack widths were obtained for each slab for different levels of applied load. It was found that the end slip was quite negligible and complete interaction on the steel decking–concrete slab interface existed at service loads and ultimate limit states. Compared to the slab with 20 kg/m3 steel fibre, the application of steel fibre in excess of 60 kg/m3 increased the rotational capacity and ultimate load by 60% and 80%, respectively. Moreover, the higher dosage of steel fibres resulted in improved crack control, as for the same level of applied load, the crack width was often reduced by 75%. However, the slabs with conventional high-strength ductile reinforcements had the greatest ultimate load and rotational capacity and exhibited the best degree of crack control with finer and more distributed cracks.

Effect of Steel Fibre Content on the Fatigue Behaviour of Steel Fibre Reinforced Concrete

Rigid pavements are widely used for very heavily trafficked freeways because of their long design period and high performance. Rigid pavements are designed for two modes of failure, namely, fatigue and erosion. Most of the fatigue damage occurs due to very heavy axle loads. In this research, steel fibre was added to Portland cement concrete at 20 kg/m3 and 60 kg/m3 to improve fatigue resistance, which could allow for thinner pavements and hence lower construction costs. In addition, the prediction of fatigue life according to the Portland Cement Association and Corps of Engineers models were compared with the measured fatigue of the plain concrete and fibre reinforced concrete. Fatigue tests were carried out using constant stress mode. A range of stresses were applied to cover a range of stress ratios from 0.26 to 0.616. Comparisons between measured fatigue lives and the predicted lives using the Portland Cement Association and Corps of Engineers models have shown that none of these models provided a good match with the measured values. It was found that steel fibres improved fatigue resistance. However, high fibre contents showed detrimental effect on fatigue at high stress ratios.

Electrochemical Corrosion Potential of Carbon Steel Feeder Pipes in a Canadian Deuterium Uranium Reactor Generating Station under Return-to-Service Conditions

Abstract One of the principle factors affecting the stress corrosion cracking (SCC) of a susceptible metal is its corrosion potential. A number of instances of cracking on the outlet feeder pipes o...