Ordinary Grout Research Articles

Seismic Performance of Precast Concrete Exterior Beam-Column Joint with Disc Spring Devices

ABSTRACT To improve the seismic performance of precast concrete reinforced frame structures which are widely used worldwide, and enable a certain repairable function for the precast structure after an earthquake, this paper proposes a new type of precast concrete frame joint using a full grouting sleeve connection with a disc spring device. The disc spring device was connected in series to the longitudinal reinforcement located in the plastic hinge zone at the beam end to provide a restoring force and protect the concrete. Six exterior beam-column joints consisting of one cast-in-situ beam-column joint and five precast concrete frame joints, using a fully grouted sleeve connection equipped with or without a disc spring device, were designed and fabricated. The failure process, hysteretic characteristics, and energy dissipation capacity of the joint specimens were analyzed based on reversed cyclic loading test. The results showed that the energy dissipation and seismic performance of the newly precast concrete joints equipped with the disc spring device were better than those of the precast concrete frame joints connected by ordinary grouting sleeves without a disc spring device. The disc spring device proposed in this study plays a similar role as a damper in the precast joint during loading and has the characteristics of concentrated damage as it transfers part of the damage in the joint core area to the built-in disc spring area at the beam end. Additionally, the deformation of the precast joints under a lateral seismic load was theoretically calculated, the calculated results were in good agreement with the experimental results.

A new grouting cable without a core tube used for reinforcement of fractured rock mass

Grouting cable is a newly developed technology for the reinforcement of fractured rock mass in coal mines of China. It integrates the procedures of cable anchoring and grouting, thus simplifying the working procedure of roadway support. However, ordinary grouting cable products with a core tube have some significant defects, such as a narrow flow channel, difficulty in slurry diffusion and significant reduction of cable strength. To overcome these shortcomings of ordinary grouting cables, this paper proposes a new kind of grouting cable without a core tube. The ordinary plastic core tube is replaced by a steel core wrapped by several steel strands. The inner gap between the steel strands and steel core is used as the slurry flow channel. The optimised measures can significantly improve slurry diffusion and strength performance of the grouting cable. As a novel idea, several samples of the new grouting cable were produced. Lab testing and field application experiment indicated that slurry diffusion and strength performance of the new grouting cable had been significantly improved compared with ordinary ones.

Study on the Evolution Law of Deep Rock Cracks and the Mechanism of Graded Gradient Support

The surrounding rock of deep roadway is mostly composed of fractured rock. The deformation of roadway surrounding rock is complicated, which not only involves the stress change, but also involves the support means. This paper aims to study the deformation and fracture evolution law of surrounding rock in deep underground engineering. According to the stress rebalancing characteristics, after roadway excavation, the development and evolution characteristics of surrounding rock cracks are studied. At the same time, different seepage zones are divided according to the relationship between surrounding rock failure and its total stress–strain, that is, complete seepage zone, seepage shielding zone, and proto-rock seepage zone. The crack distribution characteristics of surrounding rock are studied, and the graded control of gradient support is proposed. In the broken area, the gradient bearing shell outside the roadway is achieved by means of bolting and high-strength grouting. As the cracks and pore sizes in the plastic zone gradually decrease along the radial stress direction of the roadway, and the open cracks gradually change into closed cracks, it is difficult for ordinary grouting materials to complete better consolidation and filling. Therefore, small particle size grouting reinforcement materials are studied. The plastic zone (fracture zone) is reinforced with nano-scale grouting material, and the internal three-dimensional gradient bearing shell is formed by combining with the anchor cable. This research plays an important guiding role in the stability of deep roadway surrounding rock.

Research and evaluation on Water-dispersion resistance of synchronous grouting slurry in shield tunnel

When the shield tunnel passes through the watered stratum with high permeability, as the shield tail interspace prone to be filled with groundwater, resulting in the segregation and loss of ordinary grout slurry during synchronous grouting, then critically affect the physical and mechanical properties as well as the durability of the curing grouting ring. Hence, it is necessary to optimize the performance of the existing ordinary grouting slurry to improve its water-dispersion resistance on the premise of ensuring the original performance. By means of theoretical analysis and indoor tests, this paper systematically investigates the mechanism of water-dispersion resistance of synchronous grouting slurry in water-rich stratum with high permeability, establishing a set of testing process and detection method for water-dispersion resistance of synchronous grouting. Moreover, the influences of different flocculants with corresponding contents on the performance of synchronous grouting slurry have been revealed, and the evaluation criterion of water-dispersion resistance of synchronous grouting slurry in shield tunnel is also clarified. The results show that: 1) Turbidity has notable responses to the change of flocculant content, which could better reflect the clarity of water samples. So, the turbidity is considered as a main evaluation index of water-dispersion resistance of synchronous grouting; 2) On the other hand, pH and water-land strength ratio also demonstrates the acid-base changes of groundwater and the loss of cementitious materials respectively during grouting. Thus, the two indexes are applied as auxiliary evaluation indexes for water-dispersion resistance of synchronous grouting; 3) For the above evaluation indexes, corresponding critical values to satisfy the water-dispersion resistance of synchronous grouting slurry are ensured: turbidity < 100NTU, pH < 10, and water–air strength ratio at different curing ages greater than 80%.

Research on Carbon Fiber Polymer Ultrafine Cement Grouting Material

With the gradual development of deep coal mining, the demand for roadway support strength is also increasing. For ordinary grouting materials, it cannot be injected into ultra-fine pores, and the tensile strength of its consolidated body is not high. Therefore, in this paper, ultra-fine cement and carbon fiber are used as the raw materials of the grouting fluid to increase the injectability of its fine pores and the tensile strength of the consolidated body. By designing experiments with different carbon fiber content, the grouting material with the best mix ratio was formulated. The test results show that: after the grouting material is mixed with graded sand to prepare a test block, the mechanical properties of the grouting material are optimal when the carbon fiber content is 1%, and the compressive strength is 17MPa and the tensile strength is 1.34MPa.

A study on the mix proportion of fiber-polymer composite reinforced cement-based grouting material

Cement-based grouting materials are widely used to repair slab hollows under cement concrete pavement slabs. However, the existing cement-based grouting materials fail to meet the needs of rapid penetration reinforcement. In this paper, a cement-based grouting material, which is reinforced by fiber-polymer composite and with excellent characteristics of high permeability and micro expansion, is proposed to repair slab hollows between the cement concrete slab and cement stabilized base. Firstly, take the fluidity, compressive strength and flexural strength as the evaluation indexes and determine the reasonable mixing amount of each component by single mixing tests. Secondly, take the water-cement ratio, early strength agent content, modified fiber content and VAE polymer content as object factors and optimize the mix proportion of the grouting material by orthogonal tests. The effectiveness of the proposed grouting materials is identified by indoor model tests, and the results show that the mechanical properties of the proposed materials (including compressive strength and flexural strength) are improved significantly compared with ordinary grouting materials.

Experimental Study on Strength Enhancement of Expansive Grout.

Adding an expansive agent to ordinary grout can cause an expansion in volume, but also reduces its strength. In order to improve the strength of expansive grout, quartz sand is used as the strength enhancement additive. In this study, the expansion behavior and mechanical properties of the expansive grout with quartz sand are explored, through expansion development monitoring, uniaxial compression strength (UCS), acoustic emission (AE), SEM and XRD test methods. The results showed that: (1) The final expansion ratio and expansion development of the samples are related to the use of an expansive agent, but not affected by quartz sand. With the increase in expansion agent content, the average expansion ratios of the samples are 0.03%, 0.16%, 0.67%, 1.06% and 1.48%; (2) The UCS of the samples decreases with the increase in expansive agent content but increases with the increase in quartz sand content. Compared with no quartz sand, and with the increase in quartz sand content, the average strength of the samples increased by 10.51%, 29.88%, and 37.92%; (3) Quartz sand does not effectively participate in the hydration reaction, but it can effectively enhance the strength of the expansive grout without affecting its volume expansion, which makes it an ideal expansive grout strength enhancement additive.

Influence of backfilling phase change material on thermal performance of precast high-strength concrete energy pile

The use of phase change materials (PCMs) within the precast high-strength concrete (PHC) energy pile is relatively rare. A study concerning the thermal performance of the PHC energy pile backfilled with PCMs were performed to compare with conventional backfill materials. Field tests of the PHC energy pile were conducted. Then, different types of heat transfer numerical models for the PHC energy pile backfilled with water, ordinary grout, and PCMs were established, and the validities of models were confirmed by the field test data and other published studies. The following results are obtained from this study: (1) the thermal performances of the PHC energy pile backfilled with ordinary grout and PCM-type backfill materials (i.e., PCM, enhanced-PCM, and enhanced-PCM-1) are significantly greater than that backfilled with water under continuous operation; (2) intermittent operation has a larger influence on the heat exchange rate of PCM-type backfilled PHC energy pile than ordinary grout backfill material, and enhanced-PCM and enhanced-PCM-1 backfill materials generate higher heat exchange rates for the PHC energy pile than the ordinary grout under intermittent operation; (3) enhancements in the thermal properties of PCMs and intermittent operation both are important to improve the heat transfer performance of the PHC energy pile backfilled with PCMs, and the lower melting temperature of PCMs helps to enhance the thermal performance of PCM-type backfilled PHC energy pile in the cooling mode; and (4) under higher velocity of groundwater flow, ordinary grout backfill material is more suitable for the PHC energy pile compared with PCM-type backfill materials.

Field Test Research on Film Bag Grouting in Strongly Weathered Stratum Overlying Subway

A strongly weathered stratum needs to be reinforced by grouting before tunnel excavation due to its poor self-stability. This work studied the law of surface uplift caused by grouting in a strongly weathered stratum overlying a subway. A strongly weathered stratum overlying a subway section was taken as the research object, and the field test method was used to reveal the time and space variation characteristics of the surface uplift with grouting reinforcement. Then, the influence of the grouting reinforcement technology, quantity, and material on the maximum surface uplift value in the practical grouting process was analyzed. The results show the following. Regardless of whether film bag grouting is used or not, the uplift value of the monitoring points is directly proportional to time, and the growth rate of the uplift value tends to accelerate. The spatial distribution of the surface uplift is mainly related to its distance to the grouting point. In addition, the maximum uplift value of the film bag grouting technology is 32.1% lower than that of the ordinary grouting technology; given the same grouting materials and technology, the grouting amount increases by 50%, and the surface uplift value increases by 121%. Moreover, the C-S slurry exhibits rapid setting, a small diffusion range, and a large thickness of the grouting vein; the surface uplift value of the C-S slurry is 3.08 times that of the cement slurry. The field test research conclusion is applied to practical engineering, where the final uplift value is 1.8 to 2.5 cm, and the average permeability coefficient of the inspection hole is 3.52×10−7 cm/s, which reflects a good engineering governance effect.

Research on the Influence Factors of Low-Temperature Crack Resistance of Semiflexible Pavement Materials Based on Freezing Test

To study the influence factors of low-temperature performance of semi-flexible pavement materials, a freezing test was conducted, and the cracking temperature was used as the evaluation index to study the influence of asphalt type (90 matrix asphalt, SBS-modified asphalt, TPS high-viscosity modified asphalt), cement-based grout material types (ordinary grout, rubber powder grout, emulsified asphalt grout), and skeleton void ratio (20%, 24%, 28%, 32%) on the low-temperature performance of semi-flexible pavement materials. Results indicate that the freezing test can effectively distinguish the low-temperature crack resistance improvement benefits of semi-flexible pavement materials with different asphalt, cement-based grouting materials, and skeleton void ratios. Cracking temperature can effectively evaluate the low-temperature performance of semi-flexible pavement materials. The substrate void ratio is in the range of 20%-32%, and the cracking temperature changes with the increase in the substrate void ratio, decreasing initially and then rising. When the void ratio is around 24%, the best low-temperature performance of semi-flexible materials is achieved. The improvement effect of the elasticity of grout on the low-temperature crack resistance of semi-flexible pavement materials is obvious; the improvement effect of emulsified asphalt grout on the low-temperature performance of semi-flexible pavement materials is better than that of rubber powder grout. After the modified asphalt is used in the substrate, the cracking temperature is reduced by 31.4%-38.3%, which is much greater than the effect of grouting. At the same time, the elasticity of the base asphalt is more effective than the viscosity increase in improving the low-temperature crack resistance of semi-flexible materials.

Performance and Microstructure of Alkali-Activated Red Mud-Based Grouting Materials Under Class F Fly Ash Amendment

From the perspective of sustainable development and environmental protection, the environmental friendly substitute of ordinary grouting materials is needed to be proposed. In this paper, we prepared a high-performance and low-cost grouting materials from red mud, granulated blast furnace slag (GBFS) and class F fly ash (FFA). In order to determine the optimal raw materials property, we investigated the effect of FFA dosages on red mud–GBFS grouts system. The results showed that 10% of FFA content could improve the 90-day compressive strength of grouts by 15.4%; fluidity and volume stability were also improved considerably. But when the FFA content is overmuch, it would result in some negative effects, such as longer setting time and higher bleeding rate. According to the mineral phase analysis, the effects of FFA mainly attributed to the physical properties before 28 days, such as ball effect, filling effect and micro-aggregate effect, and the pozzolanic effect of FFA influenced the long-term performance chiefly. Above all the results in this study, the optimum dosage of FFA is 10%.

Ultrasonically Enhanced Physical Properties of Milky Cement for Ground Improvement

This study investigated the change created in physical properties by irradiating ultrasonic waves in Portland cement grout. In previous research, the grout equipment was scaled-up and a grout circulation system was used for the experiment. The physical properties of ordinary grout materials were compared with those irradiated by ultrasonic waves to observe its effects. This was done by analyzing and comparing the viscosity, strength and granularity. The results indicate that grout irradiated by ultrasonic waves outperformed the non-irradiated grout in all categories of physical properties.

Efficiency analysis of utilizing phase change materials as grout for a vertical U-tube heat exchanger coupled ground source heat pump system

To study the effects of using phase change materials (PCMs) as grout on the efficiency of a ground source heat pump (GSHP) system, a numerical GSHP system model was established in this study, considering both the site conditions and dynamically changing loads regulated by the heat pump. First, system efficiencies of using an ordinary grout and two other PCM grouts were investigated and compared. Second, the applicability of PCM grouts to different soil environments was investigated by analyzing the effects of subsurface characteristics on the heat exchanger efficiency. Finally, the appropriate operation mode for PCM-backfilled GSHP system was determined by comparing the effects of daily running modes with various intermittent ratios on the system performance. The results show that it is necessary to consider the effect of heat pump, especially for poor heat transfer conditions. PCM grouts with a low thermal conductivity will significantly reduce the system efficiency, whereas PCM grouts with a thermal conductivity comparable to that of an ordinary grout will improve the efficiency and operational stability of a GSHP system. A higher soil thermal conductivity and Darcy velocity improve the heat exchanger efficiency, and PCM grouts with a high thermal conductivity are more suitable for areas where the groundwater is not rich. Sufficient recovery time is necessary and important for a PCM-backfilled GSHP system to ensure operational stability and sustainability and the effectiveness of thermal radius reduction.

Mitigating shrinkage cracking in posttensioning grout using shrinkage-reducing admixture

This study aims to reduce the cracking potential of posttensioning high-performance grout (HG) through use of shrinkage-reducing admixture (SRA). With this regard, an HG mixture was initially developed to possess appropriate fluidity with low bleeding and settling. Various amounts of SRA were subsequently incorporated into the developed HG mixture at 1% and 2% by weight to the cementitious components. A widely used ordinary grout (OG) mixture was also considered for comparison. Test results indicated that the HG mixture exhibited similar flowability to the OG mixture, while imparting much better performance with regard to strength, bleeding, and settling. The addition of SRA to the HG mixture led to higher compressive and tensile strength values after 28 days, lower shrinkage strain, lower maximum internal temperature due to hydration heat, and delayed shrinkage cracking. On the other hand, the degree of restraint due to an uneven surface of duct and the filling capacity of the HG were insignificantly affected by the inclusion of the SRA. Complete filling of ducts was observed for the HG samples. The OG mixture exhibited the smallest shrinkage strain and the best performance with regard to shrinkage cracking resistance; however, the OG mixture resulted in insufficiently filled ducts, leading to atmospheric exposure of prestressing strands. Consequently, the HG mixture with 2% SRA was proposed to be most appropriate for posttensioning grout with regard to the several properties denoted above.

Experimental Study on Bleed Water of Duct Grout

For the problem of not complete filling the ducts with grout that frequent appearances in construction, the paper carried out the grouting compactness experiment of prestressed duct with kinds of grout materials produced by domestic manufacturers combining with different grouting techniques. The results indicated that all grout materials had bleed water. The ducts in test girder could not be completely filled. The vacuum-aided grouting technique’s grout bleed water is smaller than that of ordinary grouting technique, but still not be perfect. For this, the grout compacting device with independent intellectual property right is an effective measure.

Experimental Research on Interfacial Bond Performance in Rock Anchor with High-Performance Grouting Medium

There exist the problems such as low bond strength and bad durability in the ordinary grouting slurry of the ground anchor system at present. The high-performance grouting mediums RPC (Reactive Powder Concrete) and DSP (Densified Systems containing homogeneously arranged ultrafine Particles) would become the potential replacement of grouting medium in ground anchor resulting from their high compressive strength, durability and toughness. Based on a series of pull-out tests on ground anchors with different high-performance grouting medium of RPC and DSP , different bond length in the construction field, the bond performance on the interfaces between anchor bolt (deformed steel bar) and grouted medium as well as between grouted medium and rock mass was studied. The results indicate that the interfacial bond strength between RPC or DSP and deformed steel bolt ranges within 23-31Mpa, far greater than that (about 2-3MPa) between the ordinary cementitious grout and deformed steel bar. Even though the interfacial bond strength between the grouted medium and rock mass of limestone was not obtained in the test since the failure mode was pull-out of those steel bar rather than the interface shear failure between grouted medium and rock mass, the bond stress on the interface reached 6.2-8.38 MPa, also far greater than the bond strength (about 0.1-3MPa) between the ordinary cementitious slurry and rocks.