International Concrete Abstracts Portal

Multi-scale analysis, which involves combining advanced elements with computationally fast elements, is an effective method for assessing the behavior of large structures with deficient or complex members. One major challenge in multi-scale analysis is modeling the interface between the two types of elements. This study presents a new interface element for connecting a beam element to membrane elements, specifically formulated for reinforced concrete members. The proposed element considers reinforced concrete a composite material, is capable of computing linear and nonlinear stress distributions through the section, and allows for transverse expansion at the interface section. The accuracy of the interface element is verified through analysis of a series of beam specimens presented in the literature. The improvements of the proposed method are compared against two commonly used beam-membrane coupling methods. Lastly, the application of the interface element is demonstrated by multi-scale analysis of a reinforced concrete frame structure with critical joints.

Sawn joints in concrete pavements appear to be more susceptible to deterioration under cyclic freezing and thawing than formed joints. One mechanism appears to be related to water and salt solutions more readily penetrating into the concrete through the exposed interfacial transition zone (ITZ) at the saw-cut joint. This in turn will increase the risk of local expansion or dissolution around the aggregate particles at the joint face. The work described in this paper was conducted to evaluate this hypothesis. A range of concrete mixtures with different water-cementitious materials ratios (w/cm) and silica fume contents were tested in a range of deicing solutions and subjected to cyclic freezing and thawing. The data indicate that improving the quality of the ITZ does help to reduce the risk of damage. In addition, the results revealed that saturated concretes have lower freezing-and-thawing resistance compared to concrete simply soaked for a short time.

Expansion joints have been introduced using diamond wire saws in several existing concrete gravity dams to control deformations and release accumulated compressive stresses due to concrete swelling induced by alkali-aggregate reaction (AAR). Slot cuts have also been used to reduce the detrimental effects of cyclic seasonal thermal loading of dams located in northern regions. It was found, however, that it is difficult to estimate in advance the elastic rebound and long-term closure of slot walls. This paper reports field observations from cuts in three gravity dams. A complementary experimental study on four 1.5 m-long compressed concrete specimens is then presented. Measurements of elastic rebounds and long-term responses are compared with elastic and viscoelastic finite element analyses. The laboratory tests have shown that it is difficult to accurately model the long-term slot closure response, even in a controlled environment where differences from experimental measurements and numerical analyses ranging from 10 to 30% have been observed. This could be mainly attributed to sensitivity to the creep law adopted.

Section 11.7 of ACI 318-95 contains design provisions for conditions where direct shear transfer through shear-friction should be considered. Such conditions include an interface between concretes cast at different times. Shear-friction capacity is defined by this Code as a function of steel reinforcement area contained in the interface and treatment provided to the interface before the new concrete is cast against the hardened concrete. The Code also considers the presence of permanent net compression across the interface and specifies an upper limit on interface shear capacity. The test results discussed herein are used to verify and extend the application of shear-friction provisions currently incorporated in the ACI Code. Modification and expansion of the current Code are proposed in light of the additional research information available to date.

Precast, prestressed concrete voided members are used in bridge decks. All members have keyway joints which are later grouted to provide shear capacity across adjacent members. Typically a non-shrink grout is used to fill the keyway joint formed by two female-to-female shapes in the precast members. Even though these decks can be overlaid with portland cement or asphaltic concrete, these types of keyway joints often develop leaks on the underside of the bridge deck, wicking chloride laden salts into the precast concrete. Corrosion has been noted in beams adjacent to the keyway joints. Cracking in the overlay above the joint is seen in the field providing access of the chloride laden deicing chemicals or sea spray. Non-shrink grout is a poor choice for the grouting of these keyways. Designed for correction of vertical settlement shrinkage due to bleeding, these types of grouts generally develop long-term drying shrinkage upon exposure to air. Loss of interface bond between the grout and the member occurs, and shrinkage adjacent to the precast member is noticed in the field. Vertical faulting has been observed indicating a poor of load transfer across adjacent members. A lab study compared non-shrink grout with magnesium ammonium phosphate (MgNH4PO4) mortar in keyway-shaped composite specimens comprising both the grout and the keyway assembly. These specimens were initially tested in direct tension, vertical shear, and longitudinal shear. A minimum 250 percent increase in performance was observed with the MgNH4PO4 grout compared to non-shrink grout in initial tests. Longer term testing indicates virtually no loss in performance with the MgNH4PO4 keyway mortar while the non-shrink grout lost 36 percent of its initial capacity after longer drying shrinkage. Differences may be due to the better bond strength and lower drying shrinkage of these types of mortars compared to the non-shrink grouts which are in use by most DOTs in the U.S.