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The strain measurement of a 1.65-m reinforced concrete beam by use of a distributed fiber strain sensor with a 50-cm spatial resolution and 5-cm readout resolution is reported. The strain-measurement accuracy is [+ or -] 15 [micro][epsilon] ([micro]m/m) according to the system calibration in the laboratory environment with non-uniform-distributed strain and [+ or -] 5 [micro][epsilon] with uniform strain distribution. The strain distribution has been measured for one-point and two-point loading patterns for optical fibers embedded in pultruded glass fiber reinforced polymer (GFRP) rods and those bonded to steel reinforcing bars. In the one-point loading case, the strain deviations are [+ or -] 7 and [+ or -] 15 [micro][epsilon] for fibers embedded in the GFRP rods and fibers bonded to steel reinforcing bars, respectively, whereas the strain deviation is [+ or -] 20 [micro][epsilon] for the two-point loading case. OCIS codes: 290.5830, 060.2370.

A comprehensive test protocol, described in Part I of this paper, has been used to evaluate the adhesive strength, viscoelastic properties, and shear fatigue behavior of two polyurethane joint sealants for use in undoweled concrete highway joints. The results of these tests showed that the protocol was able to assist in selecting the more suitable sealant for the expected service conditions in New Brunswick, Canada. Sealant A, a coal-tar modified polyurethane with a glass transition temperature of -20.7 degrees C, showed a significantly reduced flexibility at a severe low temperature of -40 degrees C. This low temperature induced loss in flexibility was supported by the relatively low peel force required to initiate cohesive failure and the relatively high resistance to shear deflection noted with the shear fatigue test. Sealant B, on the other hand, was found to have a glass transition temperature of -43.2C and maintained its flexibility at extreme low temperatures for all dynamic tests performed. Using dynamic mechanical analysis, neither sealant showed significant degradation at high temperatures or when subjected to water or ethylene glycol exposure.

Sealants used to seal the transverse contraction joints used in joining concrete highway sections without dowels must be flexible enough to withstand excessive conditions such as large temperature fluctuations, severe pavement deflection due to heavy truck traffic, and prolonged moisture exposure. Choosing the most appropriate sealant for the expected service condition from the wide variety of sealants available on the market today can be a daunting task. In Part I of this paper, a comprehensive test protocol that correlates sealant viscoelastic properties with the sealant resistance to deflection is presented. It is proposed that the selection of a sealant should be based on a complete evaluation consisting of three test procedures: (1) the ASTM C794 adhesion-in-peel test to assess concrete/sealant adhesion; (2) dynamic mechanical analysis (DMA) to evaluate sealant flexibility by determining the glass transition temperature, T(sub g); and (3) the shear fatigue test developed by the writers to analyze sealant performance when subjected to severe pavement deflection in combination with various environmental conditions. Part II of this paper will present the results of testing and comparison of two polyurethane joint sealants using this proposed test protocol.

Time-dependent distributions for temperature and moisture content in a concrete wall subjected to fire are determined by a model of heat and mass transfer in porous media. Free-water flow, bound-water diffusion, gas-phase flow, water-vapor diffusion. and thermal energy arc accounted for in the model. The governing transient differential equations are discretized by a control-volume formulation reported by Patankar in 1980, and solved in time using a fully implicit scheme. Two different fire exposure curves (namely, standard curve according to ASTM E-119 and a more realistic curve reported by Ellingwood in 1991) are employed in the analysis. The assessment of two simplified models, in which all pore water is assumed to evaporate at 100 [degrees] C, is performed b comparing their predictions to the full analysis. For temperature and saturation, the time developments predicted by the two simplified models and by the full analysis present similar trends; however, the simplified models seem t be appropriate only for very preliminary fire safely analyses, since they tend to underestimate temperatures.

In marine concrete structures, construction joints, formed at the intersect of the end of one concrete placement and the beginning of a new placement, have been identified as vulnerable zones that may permit the intrusion of chlorides over a relatively small area of the reinforcement, thus accelerating corrosion. The present paper reports a research study to evaluate the effectiveness of calcium-nitrite corrosion inhibitor in combination with pulverised fly ash on the corrosion protection of reinforced concrete slabs manufactured with a construction joint intersecting the reinforcement at right angles and exposed to a marine environment for seven years. Electrochemical testing, chloride profiling using the scanning electron microscope/energy dispersive X-ray analyser and assessment of the damage caused by chloride-induced corrosion on the reinforcing bars, were conducted. Results showed that bars retrieved from low water/cementitious material ratio concretes containing calcium nitrite and fly ash experienced negligible corrosion damage; conversely, in specimens prepared with high water/cementitious material ratio, this combination provided a low level of protection. [ABSTRACT FROM AUTHOR]

Brillouin scattering based sensors can measure strain and/or temperature at all points along an optical fiber; first, the fiber must be calibrated. A problem arises because the temperature coefficient of a fiber bonded to a host is changed by the host structure. Using the loose fiber coefficient could lead to large strain and temperature measurement errors. This article studies the change in the Brillouin temperature coefficient due to bonding. The intrinsic Brillouin temperature coefficient of two fibers is also found. This coefficient allows accurate strain and temperature measurements to be made, assuming the coefficient of thermal expansion of the host is known. [ABSTRACT FROM AUTHOR]

Abstract: This communication presents the results of T 2-weighted nuclear magnetic resonance imaging (MRI) of a water saturated porous volcanic rock using a fast single point imaging technique (turboSPI). Imaging porous materials with heterogeneously distributed mineral products, and air voids, using conventional imaging methods, which introduce T 2-weighting by increasing the time between the excitation and refocusing pulses, often results in high diffusive signal losses and susceptibility distortion. T 2-weighted images acquired of a water saturated porous rock using turboSPI with an effective echo time of 8.1ms (actual inter-echo time of 0.9ms) exhibit significantly decreased diffusive attenuation, compared to analogous images obtained with an inter-echo time of 8.1ms. [Copyright &y& Elsevier]

Studies the effect of calcium nitrate-based corrosion inhibitor and fly ash on compressive strength of high-performance concrete. General factors affecting strength of concrete; Corrosion inhibitor amount.

Nuclear magnetic resonance (NMR) relaxation time mapping in partially dried mortar is presented. Relaxation times in concrete are typically multi-exponential, and exhibit highly effective relaxation mechanisms (T[sub IL] ≈ 3 ms, Δv[sub ½] ≈ 2500 Hz). One-dimensional mapping of the spin-lattice relaxation time is used to study relative changes in the water-occupied surface-to-volume ratio, as a function of mixture conditions, initial hydration period, and drying time. These results provide evidence for a penetrating microcracking phenomenon, due to local drying-induced tensile stresses. This conclusion was further supported by a relaxation time study of samples which were preconditioned so as to be at equilibrium with various relative humidities. [ABSTRACT FROM AUTHOR]