Concrete Grout Research Articles

Experimental Study of a Large-Scale Ground Anchor System with FRP Tendon and RPC Grout Medium

The poor performance and durability of traditional steel tendon and cement grout have become serious constraints to the development of ground anchor systems, especially when these systems are permanent features in large-scale projects such as ground anchors with capacities of more than 4,000 kN in Aizhai Bridge, China. This paper presents a large-scale ground anchor system with carbon fiber-reinforced polymer (CFRP) tendon and reactive powder concrete (RPC) grout as the bonding media in both above-ground and below-ground parts. Two full-scale ground anchor specimens named GA12-20 and GA12-9 were designed and installed at the construction site, and their behavior was systematically studied through monotonic and cyclic load testing. The two systems displayed acceptable displacements under both monotonic load testing with maximum tension twice the design lock-off load and in cyclic load testing under about 90% of its bearing capacity, with residual displacements all less than 5 mm. Furthermore, the bond stress distributions in the grouted portions of the rods in tendon showed both systems have reliable bonding capacities under tension. This innovative ground anchor system with CFRP tendon and RPC grout showed a good behavior and successfully served as the ground anchor of the Aizhai Bridge.

Performance of Concrete Grout under Aggressive Chloride Environment in Sabah

Service life of existing reinforced concrete (RC) structures in coastal towns of Sabah has been affected very much. Concrete crack, spalling of concrete cover and reinforcement rusting of RC buildings are seen even within 5 years of construction in Sabah. Hence, in this study a new mix design of concrete grout was developed using locally available materials and investigated under two curing conditions and workability, compressive strength, Accelerated Mortar Bar Test (AMBT), water absorption, volume of permeable voids (VPV), Sorptivity and 90-days salt ponding test were conducted. The compressive strength of concrete grout at the age 90 days was found to be 44.49 N/mm 2 under water curing. It was observed that the percentage of mortar bar length change was below 1% for developed concrete grout. The water absorption of the concrete grout was in between the range of 0.88 % to 3.60 % under two different curing up to the age 90 days. It was also observed that the VPV of concrete was in the range of 0 % to 9.75 and 2.44% to 13.05% under water curing and site curing respectively. It was found that the Sorptivity of the concrete grout under water curing at the age of 28 days is 0.211mm/√min and at the age 90 day are 0.067 mm/√min. The chloride content decreased greatly, 90% after a depth of 15 mm. It was noticed that the site cured samples showed higher chloride contents near surface compared to water cured samples. This investigation suggested that the developed mix design of concrete grout using locally available construction materials can be used for crack repairing of existing RC structures in Sabah. Keywords—Concrete grout, Salt ponding, Sorptivity, Water absorption.

Compressive strength of micropile-to-grout connections

Strengthening foundations with micropiles is progressively being used, due to the major advantages that this technique presents. Nevertheless, the influence of some relevant parameters in the overall behavior of the retrofitted foundations has not yet been studied. Generally, micropiles are installed in holes drilled through the existing RC footing, which are then filled with grout. The efficiency of the load transfer mechanism depends on the bond strength of both the micropile–grout and the concrete–grout interfaces. This paper describes an experimental study performed to specifically study the influence of the following parameters on the bond strength between micropile–grout interface: hole diameter; embedment length of the micropile; and level of confinement of the grout mass. Thirty micropile–grout specimens were submitted to monotonic push-off tests, until failure. Bond strength was found to increase with a decrease of the hole diameter and with an increase of the confinement level.

STRUCTURAL PERFORMANCE OF REINFORCED CONCRETE MASONRY BEARING WALLS AND WALL GIRDERS USING SMALL-SIZE CONCRETE UNITS

The authors have been developing reinforced concrete masonry buildings with the wall thickness of 150mm, for the purpose of the increase of inner space of buildings, the decrease of building weight, and the usage of the standard building module of 300mm. In this paper, test results of laterally loaded bearing walls and wall girders with the standard reinforcement, using newly developed small-size concrete units with the thickness of 150mm, special pre-mixed cement mortal for the joints, and grout concrete of the strength of 60 N/mm2 class, are shown in detail.

Bonding stress—slip constitutive behavior between bars and grout concrete

To establish bonding stress—slip constitutive model between bars and grout concrete, 13 test specimens were employed to study the bonding behavior and the force transfer of bars adhered to grout concrete. The bonding stress development of bars adhered to grout concrete was analyzed. The local bonding stress—slip curve was obtained. Based on the test results, a new bonding stress—slip constitutive model between bars and grout concrete was proposed. The results show that the maximum bonding stress is not influenced by the bar bond length, but it is strengthened when the splitting strength of grout concrete is increased. The model matches the experimental results well, and the regressing coefficient equals 1.7.

Flexural behavior of precast concrete box beams posttensioned with unbonded, carbon-fibercomposite cables

A common problem in prestressed concrete box - beam bridges is the corrosion of steel reinforcement due to seepage of moisture and chemicals through longitudinal cracks in the deck slab between adjacent beams. Replacing conventional steel reinforcement with non-corroding fiber-reinforced-polyrner -(FRP) reinforce-ment eliminates the corrosion potential in the concrete of box-beam bridge systems that are reinforced with prestressed carbon-fiber-composite cables. Three box-beam bridge models were designed, constructed, instrumented, and tested to failure. The three bridge models had the same cross section and dimensions. Each bridge model was formed by aligning two -precast, prestressed concrete box beams adjacent to each other, filling the gap between the beams with concrete grout, applying transverse post-tensio, and casting a common deck slab. Each bridge model was reinforced with 14 bottom pretensioned strands 14 top nonprestressed strands, and 8 bottom nonprestressel strands. Two of the bridge models contained 12 unbonded longitudinal strands, which were post-tensioned for only one of the models. The third bridge model did not contain any unbonded longitudinal strands. Generally, the model that includ unbonded longitudinal post-tensioning demonstrated improved flexural behavior and minimized deflections.

Stereological Analysis of Aggregate Distribution in Contaminant Barrier Concrete

The distribution of large aggregate particles in concrete is a significant determinant of concrete strength, durability and wave/fluid transmission characteristics. These characteristics are important with respect to the performance of concrete containment systems for interim storage of radioactive waste. Even distribution of aggregate particles within concrete matrix promotes spatial uniformity of concrete characteristics and minimizes the weakness that can develop in aggregate-deficient portions. The internal heterogeneity of concrete can be assessed destructively through standard load testing or indirectly through imaging and stereological analysis of obtained images. In this paper, an indexing methodology is developed and applied to the analysis of the areal and volumetric distribution of aggregates in samples extracted from hardened concrete grout for waste storage. Analyses of 301 mm mini-slices that were reconstructed into 4 full slices on the basis of a fixed aggregate diameter of 16.93 mm indicate a statistical goodness of fit χ2 value of 4, which is below the 5% significance level (18.3). This result indicates no significant unevenness in the spatial distribution of aggregate particles in the concrete grout. The results demonstrate that this stereologically based approach is useful in quality assurance assessments of emplaced concrete.

小型コンクリートユニットを用いたＲＭ組積体の面外曲げ性状

The authors have been developing low-rise reinforced concrete masonry buildings with the wall thickness of 150mm, for the purpose of the increase of inner space of buildings, the decrease of building weight, and the usage of the standard building module of 300mm. In order to realize the buildings, out-of-plane bending behaviors of fully grouted concrete masonry prisms, using newly developed small-size units with the strength of 40 N/mm2 class and grout concrete of the strength of 40 - 60 N/mm2, were investigated. Special pre-mixed cement mortal was used for the joints to obtain high out-of-plane bending performance.

小型コンクリートユニットを用いたＲＭ組積体の圧縮性状

The authors have been developing low-rise reinforced concrete masonry buildings with the wall thickness of 150mm, for the purpose of the increase of inner space of buildings, the decrease of building weight, and the usage of the standard building module of 300mm. In order to realize the buildings, compressive behaviors of fully grouted concrete masonry prisms, using newly developed small-size units with the strength of 40N/mm2 class and grout concrete of the strength of 40-60N/mm2, were investigated. Special pre-mixed cement mortal was used for the joints to obtain high out-of-plane bending performance.

Waved Joint for Seismic-Resistant Precast Floor Diaphragms

Floors made of precast concrete hollow-core slabs may be constructed without a structural concrete topping and with transverse tie reinforcement placed only out of the slabs. Longitudinal joints between adjacent precast units are filled with mortar on site. To ensure good diaphragm performance under seismic action, a special joint has been devised, in which the slab sides are profiled as continuous sinusoidal waved shear keys. The research involved experimental investigations and analytical modeling. The features of the joint and the means of production were first worked out. Then, a series of destructive tests were performed, on both short joint samples and full-scale floors, made of extruded prestressed hollow-core slabs without topping, all subjected to large in-plane loading reversals. They showed that, after the adhesion between the grout and precast concrete is overcome, a stable cyclic shear transfer mechanism develops, based on wedge action and friction raised at the wavy slab–mortar interface. Th...

Effectiveness of Composites in Earthquake Damage Repair of Reinforced Concrete Flared Columns

A method to utilize fiber composites for rapid repair of earthquake damaged flared columns was developed. Two 0.4-scale reinforced concrete columns that had been tested to failure in previous research were used. Both columns had been subjected to slow cyclic loads and had failed due to low-cycle fatigue of the longitudinal bars. To repair the columns, the damaged concrete in and around the plastic hinge was removed and the steel bars were straightened. Low-shrinkage, high-strength concrete grout was placed in the column afterward. The broken longitudinal bars were not replaced. Rather, glass and carbon fiber reinforced polymer (FRP) sheets with fibers running in the axial direction of the column were added to provide flexural strength to the columns. Additionally, glass FRP sheets with horizontal fibers were attached on the column to provide confinement and shear strength. Cyclic tests of the repaired columns indicated that the method to restore the strength was effective. Analysis using conventional constitutive relationships led to a close estimate of the lateral load response of the models.

An Investigation of the Effects of Water Content on the Shielding Performance of the Primary Upper Shield in the High Temperature Engineering Test Reactor (HTTR)

High Temperature Engineering Test Reactor (HTTR) is the first High Temperature Gas-cooled Reactor in Japan. The plant layout and radiation shielding are designed so that the plant can be operated without any employee receiving a high radiation dose rate. The primary upper shield of HTTR is composed of concrete (grout) and carbon steel. The function of the primary upper shield is to attenuate neutrons and gamma rays generated in the core to satisfy dose rate criterion for the operating floor. Since the HTGR uses high temperature helium as coolant, temperatures of shielding materials could be higher than that of conventional reactors. According to the analytical simulation, the maximum temperature inside of the primary upper shield during full-power operation was estimated to be about 85 °C. Since water content in the primary upper shield concrete depends on its temperature, shielding performance of the concrete under HTTR operational conditions need to be confirmed. Thus the water content of the concrete was experimentally investigated by out-of-pile heat-up tests to 175 °C. According to these tests, a water release model was developed. The out-of-pile heat-up tests showed that the water content in the concrete was larger than 78 kg/m3 up to 110 °C in a 95 % confidence limit.

The numerical modelling of crater repairs in airfield runways

This paper describes the numerical modelling of the repair of an explosively formed crater. The crater is repaired by infilling with compacted material and covering the repair with a layer of rapid setting flood grout concrete. The paper suggests minimum Young’s modulus requirements for the crater infill and for the flood grout. The results show that a load distributed between two wheels produces lower runway deflections and stresses than the same load on a single wheel. Three further research areas are identified: first, laboratory testing of flood grout less than 1 h old; second, the establishment of the relationship between the Young’s modulus, compressive strength and flexural strength of the flood grout up to 28 days old; and third, the interface effects between the crater repair and the existing runway.

Chemical reaction between concrete and natural groundwaters and its implications for the commissioning of observation boreholes in chalk

Abstract Four purpose-constructed observation boreholes in chalk were found to contain water with pH of 10-11.5 and abnormal chemistry within fourteen months of commissioning. Experiments show that this was due to contamination by alkaline porewater solutions from the concrete grout used in construction. Contamination was still detectable nearly three years after construction but was cleared by pumping. A six-hour pumping test is recommended as standard procedure during commissioning of observation boreholes.

Cavity at Keban Dam, Turkey

The Keban Dam was completed in 1974 on the Euphrates River in the eastern part of Turkey. The main dam of rock fill and concrete gravity structures rests on a karstic marble and limestone. The so-called ”Crab Cavity”, which was found during the construction in 1971, is the largest cavity encountered in the foundation of Keban Dam, on the left abutment and about 320 metres below the crest level. The volume of the cavity was estimated to be about 104 000 cubic metres. The cavity was plugged by using approximately 63 400 cubic metres of tremie concrete, slurry and neat grout, which plugged the downstream half part of it.