International Concrete Abstracts Portal

Wet-mix shotcrete has been used more and more for structural applications in the past few decades. Recently, wet-mix shotcrete was successfully used to construct a mass structural wall with congested reinforcement and minimum dimensions of 1.0 m in a sewage treatment plant. A low-heat shotcrete mixture that included up to 40% slag was proposed for shotcrete application. A preconstruction mockup was shot to established proper work procedures for shotcrete application and qualify the shotcrete mixture and shotcrete nozzlemen. Extraction of cores and cut windows from the mockup confirmed proper consolidation around the congested reinforcement. A thermal control plan was developed, which included laboratory and field testing requirements, thermal analysis modeling with a three-dimensional (3-D) finite element program, and thermal control requirements, including installation of cooling pipes and thermal blankets. Shotcrete proved to be an efficient means for mass concrete structural construction. Thermal control for mass shotcrete construction was studied, and the proposed thermal control plan was proved to function properly. The general guidance for mass shotcrete construction is provided.

This paper aims to find the effects of viscosity on concrete behavior in pipelines. Concrete was prepared according to ACI 304.2R-96. Experiments were conducted for measuring its workability by means of slump test. Fluidity and rheology measurements of fresh mortar were investigated. The concrete behavior in pipes was directly investigated using computational fluid dynamics (CFD) simulation, which is based on the Eulerian approach and the dense discrete phase model (DDPM). Concrete behavior including flow profiles, aggregate distributions, and migration was analyzed and discussed. It was observed that the flow characteristic varies from shear flow to plug flow with increased viscosity, and the aggregate distribution along the central axis is more homogeneous. Aggregate radial migration is more pronounced with increased shearing time, decreased viscosity, and enlarged size of aggregates. It was also found that concrete between 12 and 22 Pa·s (1.74 × 10–3 and 3.19 × 10–3 psi·s) is more suitable for pumping.

Double-beam coupling beams (DBCBs) are a viable alternative to diagonally reinforced concrete coupling beams (DCBs). While construction time and effort of DBCBs is much less than DCBs, their ability to sustain strong earthquake forces was also experimentally proven to be equivalent to DCBs. DBCBs consist of two slender reinforced concrete beams with an unreinforced concrete strip (UCS) between them. A DBCB gradually splits into two slender beams from small to large displacements, thereby transitioning from a brittle shear mechanism to a ductile flexural mechanism. This paper presents a recommended design procedure for DBCBs based on previous experimental results. An additional specimen was designed based on the design recommendation and tested under the same displacement protocol. The specimen showed satisfactory seismic performance with ductile behavior up to 6% beam chord rotation. One of the major advantages of DBCBs is they allow utility ducts such as polyvinyl chloride (PVC) pipes to pass through the coupling beams at the UCS. Experimental testing and nonlinear finite-element analyses reveal that the location of the utility ducts can have a significant effect on the behavior of DBCBs. Research results suggest that these utility ducts should be placed at the ends of the UCS. Prior experimental testing indicated that when the span-depth ratio ln/h of a DBCB becomes smaller, the load-versus- beam chord rotation response exhibits a pinched shape due to the greater influence of shear cracks. This pinching effect was investigated by nonlinear time-history (NTH) analyses on a 42-story coupled wall system subjected to both design-basis earthquakes and maximum-considered earthquakes. A hybrid model for DBCBs considering shear, flexure, and pinching was developed. The NTH analyses show that the seismic performance in terms of peak interstory drift ratios is nearly identical between DBCBs and DCBs; therefore, no evidence indicates pinching having an appreciable effect.

Synthetic fibers have been recently used to enhance the ductility, durability, flexural strength, and shear strength of concrete pipes while reducing the steel reinforcement. However, using the same pipe wall thickness specified by ASTM standards did not result in a significant enhancement in the flexibility of fiber-reinforced concrete pipe. This research investigates the effect on the flexibility, strength, stiffness, and strain capacity of using minimal steel reinforcement with the polypropylene fiber-reinforced concrete pipe with reduced wall thickness. Concrete pipes with diameters of 1200 and 1500 mm (48 and 60 in.) with respective wall thicknesses of 50 and 63 mm (2 and 2.5 in.) were tested under a three-edge bearing load. To assure maximum fiber contribution to pipe strength, a 9 kg/m3 (15 lb/yd3) fiber dosage was used with different amounts of steel reinforcement. Results showed that all tested pipes surpassed 5% deflection of their inside diameter with high load capacity. The tested pipes exhibited flexural failure, and at higher loading levels, radial and shear failure modes were also observed. Concrete pipe with a diameter of 1200 mm (48 in.) reinforced with steel area of 10.2 cm2/m (0.48 in.2/ft) fulfilled the ultimate strength requirements of ASTM for Classes I, II, and III. Also, concrete pipe with a diameter of 1500 mm (60 in.) reinforced with a steel area of 8.9 cm2/m (0.42 in.2/ft) did not fulfill the ultimate strength requirements of ASTM for Classes I and II. These pipes exhibited stiffnesses as high as 7.8 and 10.2 times that of high-density polyethylene pipe at 5% deflection for diameters of 1200 and 1500 mm (48 and 60 in.), respectively. Increasing steel area also increased the strain capacity of the pipes. Also, comparing with past research, increasing fiber dosage from 4.75 to 9 kg/m3 (8 to 15 lb/yd3) increased the stiffness by 95%.

The performance of steel pipelines embedded in various backfill materials under seismic wave propagation was evaluated using a three-dimensional (3-D) finite element (FE) model. Four different soils and three selected controlled low-strength material (CLSM) mixtures were evaluated as backfill materials. Effect of various model parameters on calculated pipe stresses were analyzed. Predicted pipe stresses were compared to pipe stresses calculated using the American Society of Civil Engineers (ASCE) guidelines. ASCE guidelines are developed for pipes embedded in soils and are valid only for specific assumptions. After setting the model parameters to match the predicted stresses by the ASCE guidelines for pipes embedded in soils, the developed FE model was used to evaluate the CLSM mixtures under various pipe end conditions. Results indicate that the use of a CLSM mixture instead of compacted soils as a backfill material can significantly reduce the stresses of embedded pipes under seismic wave propagation.