Design and construction application of concrete canvas for slope protection

doi:10.1016/j.powtec.2018.12.075

Powder Technology

Volume 344, 15 February 2019, Pages 937-946

https://doi.org/10.1016/j.powtec.2018.12.075 Get rights and content

Highlights

•
SSRFEM is used to evaluate the performance of CC slope protection.
•
The stability of CC slope protection at early curing age is analyzed.
•
The stability of CC slope protection for rainfall condition is analyzed.
•
FRP reinforced CC is used to extend the application of CC in slope engineering.

Abstract

Concrete canvas (CC) has the potential to become a widely used slope protection material owing to advantages such as flexibility, fast construction with low labor costs, and quick strength development. This article studies the mechanical properties and stability of CC slope protection by comparing it with conventional material (shotcrete). The compressive strength development and tensile strength of CC are first tested. To further improve the tensile strength of CC, an Aramid fiber reinforced sheet (called AFRP) is glued to the surface of CC. The tensile and shear behaviors of FRP-reinforced CC are investigated as well. Then, a finite element model is used to simulate the stability of the slope of CC (FRP-reinforced CC) and shotcrete with different curing times and the stability of CC slope protection under heavy rainfall. The results indicate that FRP-reinforced CC can satisfy the design requirements of slope protection when the height of the slope is below 10 m. Compare with traditional cementitious material (e.g., shotcrete), CC provides a more suitable solution for the rapid and abominable (e.g., heavy rainfall) construction of slope protection.

Graphical abstract

Introduction

Over the past decades, one of the most important research object is to improve the mechanical properties of cement to adapt to the more complex construction environment. New materials are constantly being applied in construction to reduce the environmental impact. Among them, concrete canvas is an ideal construction material for slope protection.

Concrete canvas (CC), invented by Brewin and Crawford in 2004 in the UK, is part of a new class of revolutionary construction materials called geosynthetic cementitious composite mats (GCCMs). CC is a flexible, cement-impregnated fabric that hardens on hydration to form a thin, durable, waterproof and fire-resistant concrete layer [1]. Recently, Bao [2] and Han et al. [[3], [4], [5]] revealed that the mechanical strength and volume stability of CC were directly affected by the properties of the components, including the type of cement matrix, type of fiber, and geometric pattern of the fabric.

Normally, cloth-like CC is rolled up and sealed in a package by the manufacturer. It can be transported to the deployment site for easy utilization. CC allows for construction without the need of mixing/casting/finishing equipment or a framework. The engineer can position CC on the surface of the target easily, and just spray water. After the CC hardens, it forms a rigid protection layer. Compared with traditional materials for slope protection layers (e.g., shotcrete layers), CC is faster, easier, and more cost-effective product to install, and has excellent benefits of reducing the environmental impact, shortening the construction period, and lowering labor costs. For durability, CC is twice as abrasion resistant as standard OPC concrete, has excellent chemical resistance, good weathering performance and will not degrade in UV. CC shows high durability with minimum 50 year expected life. In addition, CC has excellent impermeability, the permeability of material mainly depends on the particles size, the density of particles, the shape of particles or the pore structure around aggregates [[6], [7], [8], [9]]. Since the usage of fine particle cement powder and the fully hydrated of cement powder, the matrix of CC after hydration is very dense and the permeability (k-value) of CC can reach between 10⁻⁸ and 10⁻⁹ m/s. More important, CC has a significant advantage for the rapid construction of slope protection [10] when the construction environment is severe and complex (i.e., emergency construction of slope protection or heavy rainfall).

At present, slope stability is usually evaluated by using limit equilibrium methods (LEM) or finite element model (FEM), and the seepage field is often estimated by various simplified methods in geotechnical engineering practice. The most difficult problem in using the displacement-based FEM for a stability analysis is in calculating the factor of safety. This difficulty can be overcome by introducing an FEM with a shear strength reduction technique (SSRFEM), which was proposed as early as 1975 by Zienkiewicz et al. [11]. Numerical examples that have appeared in the literature show that SSRFEM is an effective method for assessing the factor of the safety of slope and for locating the failure surface [12,13]. Cai and Ugai [14] utilized SSRFEM to investigate the stability of slopes under rainfall by analyzing the transient water flow through unsaturated-saturated soils. Huang et al. [15] investigated the accuracy of the technique and compared it with a solution from conventional limit equilibrium methods for soil slopes under transient seepage.

CC has been increasingly used for slope protection. However, to the authors' knowledge, little research works on the geotechnical behavior of CC slope protection can be found in the literature. To form a design basis for the application of CC in the field of slope protection, this paper carries out a study on the design and performance evaluation of CC slope protection. First, a series of experiments are carried out to investigate the compressive strength development, tensile strength, and shear strength of CC and FRP-reinforced CC. Then, a brief description of the construction process of CC slope protection is presented. Finally, a finite element model is used to evaluate the stability of a slope protected by CC and FRP-reinforced CC layers. The tensile stress, shear stress, and displacement of CC and FRP-reinforced CC layers are analyzed, the simulation results are compared with the tensile and shear strengths of CC and FRP-reinforced CC. The stability of the slope of CC and shotcrete with different curing times, and the stability of CC slope protection under heavy rainfall, are also investigated.

Section snippets

Mechanical properties

Shotcrete is an engineered material that has been extensively used for the rapid construction of embankment slopes in highway engineering works. In this section, the constitution and preparation process of CC and FRP-reinforced CC are presented. Then, the compressive strength development, the tensile and shear behaviors of CC and FRP-reinforced CC are tested to make a comparison with shotcrete.

Slope stability analysis

Owing to the characteristics of flexibility and light weight, the typical construction speed (as shown in Fig. 6) of CC slope protection is 200 m²/h by a three-man team. The use of AFRP and 3D spacer fabric will inevitably lead to an increase in material costs; but significantly reduce both construction cost and curing cost, for instance, safe and easy to install due to the flexibility of CC, quick construction with very low labor cost, unnecessary extra moisture curing, unnecessary framework

Conclusions

The features of rapid hardening, high early-age strength, and low construction costs of the CC product make it very suitable for application of slope protection. FRP-reinforced CC has high tensile strength and extends the application of CC in slope engineering. In this paper, the compressive strength development of CC and the tensile strength of CC and FRP-reinforced CC are tested to investigate their basic mechanical properties. The stability of CC and FRP-reinforced CC slope protection in

Acknowledgments

The authors gratefully acknowledge the financial support of the National Nature Science Foundation Project of China (Grant No. 518781521 and No. 5146113500), the Ministry of Science and Technology of China's “973 Project” (Grant No. 2015CB655102).

References (29)

F. Han et al.
Influences of geometric patterns of 3D spacer fabric on tensile behavior of concrete canvas
Constr. Build. Mater.
(2014)
J. Lin et al.
Effect of particle morphologies on the percolation of particulate porous media: a study of superballs
Powder Technol.
(2018)
W. Xu et al.
Random non-convex particle model for the fraction of interfacial transition zones (ITZs) in fully-graded concrete
Powder Technol.
(2018)
H. Li et al.
Application design of concrete canvas (CC) in soil reinforced structure[J]
Geotext. Geomembr.
(2016)
J.Z. Ma et al.
Identification of representative slip surfaces for reliability analysis of soil slopes based on shear strength reduction
Comput. Geotech.
(2017)
M. Huang et al.
Strength reduction FEM in stability analysis of soil slopes subjected to transient unsaturated seepage
Comput. Geotech.
(2009)
M.C.G. Juenger et al.
Advances in alternative cementitious binders
Cem. Concr. Res.
(2011)
J. Wang et al.
Microstructure, permeability and mechanical properties of accelerated shotcrete at different curing age
Constr. Build. Mater.
(2015)
F. Zhang et al.
Experimental study of the mechanical behavior of FRP-reinforced concrete canvas panels
Compos. Struct.
(2017)
E. Damiano et al.
Investigation on rainwater infiltration into layered shallow covers in pyroclastic soils and its effect on slope stability
Eng. Geol.
(2017)

C.W.W. Ng et al.

A numerical investigation of the stability of unsaturated soil slopes subjected to transient seepage

Comput. Geotech.

(1998)

S. Oh et al.

Slope stability analysis under unsaturated conditions: case studies of rainfall-induced failure of cut slopes

Eng. Geol.

(2015)

J.M. Gasmo et al.

Infiltration effects on stability of a residual soil slope

Comput. Geotech.

(2000)

J. Zhang et al.

Probabilistic prediction of rainfall-induced slope failure using a mechanics-based model

Eng. Geol.

(2014)

Cited by (36)

Mechanical performance of concrete canvas reinforced with insert-bar structures under quasi-static and impact loading
2023, Construction and Building Materials
Concrete canvas (CC) is a promising composite based on a combination of three-dimensional fabric and cement-based powder, with the comprehensive advantages of easy storage and transport, convenient construction, rapid strength development, and low dust pollution. In civil and military engineering, interest and exploration work within the field of CC have been ongoing for many years. While external measures exist to enhance the mechanical properties of CC, substantial internal measures are still lacking. In this paper, an internal stiffening strategy was proposed by coupling warp-knitted spacer structure with a series of insert-bar structures, attempting to improve the mechanical performance of CC. The reinforcing effect of flexible bar stiffeners were investigated through quasi-static bursting test and impact test. Damage morphology analysis was then performed to reveal the progressive failure mechanism. The obtained results demonstrated that flexible bar stiffeners with low modulus were highly beneficial reinforcements for CC due to their favorable synergy and great stress dissipation capacity. The load-bearing capacity and toughness of CC were increased with the insertion height and groups of bar combination. The vertical combination could further enhance the penetration resistance by altering stress transfer.
Recent advances in slope stabilization using porous vegetation concrete in landslide-prone regions: A review
2023, Journal of Building Engineering
The risks of soil erosion and landslides in tropical regions are severe. They are triggered mainly by excessive rainfall, which leads to a pore water pressure spike and a lower shear strength of earth materials. In recent years, there has been a growing interest in the application of durable, economical, and sustainable slope stabilization technologies, and porous vegetation concrete (PVC) has proven to be a promising solution. The PVC technique incorporates both porous concrete and vegetation. Combining these two materials aims to achieve dual benefits: immediate slope protection from porous concrete and continued vegetation growth, which positively influence the mechanical and hydrological properties of the slope and enhance its aesthetic appeal. This review presents the latest advancements in the use of PVC for slope stabilization, focusing on material mix designs and properties (porosity, strength, pH, and durability), challenges hindering its effective implementation, such as the type and quantity of vegetation seeds compatible with porous concrete, and prospects for future studies that could improve its application. Furthermore, it highlights the advantages and disadvantages of other slope stabilization techniques. This review serves as a valuable resource for practitioners, researchers, and policymakers to implement new methods of slope protection using PVC.
Mechanical properties and microstructure evolution of two ecological slope-protection materials under dry-wet cycles
2023, Journal of Cleaner Production
Owing to the occurrence of rain and heat during the same period in the Loess Plateau, the strong dry–wet cycle results in shallow damage such as erosion. As a result, applying new ecological protection technologies has become important in solving this problem. In this study, polypropylene fiber and guar gum were mixed with loess in a certain proportion to form two kinds of slope ecological protection materials, i.e., polypropylene fiber reinforced soil (PFS) and guar gum mixed soil (GGS). Sixteen dry-wet cycle tests were carried out on the two slope protection materials, and the shear mechanical tests were conducted on the samples after cycling. On this basis, the microstructure evolution characteristics of the samples were observed by scanning electron microscope. Results showed that the mechanical properties of the two slope protection materials deteriorated after 16 dry-wet cycles. Among them, the c and φ of PFS under the three levels of water content decreased by an average of 21.3% and 8.9%, respectively, whereas GGS decreased by 55.8% and 21.7%, respectively. Moreover, the mechanical deterioration characteristics of the two slope materials showed strong unity with their internal microstructure. The field tests of the two slope protection materials both performed good ecological protection effect, and the deterioration process was in good agreement with the laboratory phenomena. The microscopic action mechanism inside the material was closely related to the macroscopic performance. Polypropylene fiber can act as a “bridge” among soil particles to prevent the development of cracks, and guar gum and its hydration products can enhance the cementation among soil particles. This study could provide reference for further combining the two materials reasonably, using their respective advantages and improving the ecological protection effect of loess slopes.
Soil stabilization using synthetic polymer for soil slope ecological protection
2023, Engineering Geology
Polymer treatment can protect soil slopes by enhancing topsoil macro-properties and promoting vegetation growth. In the present study, laboratory and field application tests were performed on polyurethane (PU)-treated soil to investigate its effect on soil slope ecological protection, and the mechanism related to achieving the ecological protection of soil slopes was revealed. Laboratory tests show that PU addition could greatly enhance the unconfined compression strength of silty sand and its tensile and shear strengths, especially the first two, which increased from about zero to 952.61 and 211.47 kPa, respectively. The addition of PU also led to a reduction in permeability and an enhancement in water retention capacity. The permeability coefficient decreased by an order of magnitude, whereas the water retention capacity remained at a high and stable level for a long period with little water supplementation. In addition, the PU-treated soil showed satisfactory erosion resistance and protected vegetation growth to some extent, both depending on the amount of PU, whereas a competitive relationship was observed between the contribution of the PU amount to anti-erosion and the environment for plant growth caused by the PU content. Field observations showed that PU treatment could effectively and ecologically protect soil slopes by enhancing topsoil erosion resistance, mechanical strength, and water retention, thereby accelerating vegetation growth and cover. The PU stabilization effect benefits from the improvement in the microstructure of silty sand caused by PU adsorption, connection, and filling effects. This induced a denser and stiffer whole that covered on the slope surface, which, on the one hand, enhanced the stability of the slope surface and weakened the influences induced by rainfall and runoff and, on the other hand, promoted vegetation growth by reducing soil erosion and providing moisture.
Experimental study on the mechanical properties of concrete canvas and CFRP jointly confined circular concrete columns under axial compression
2023, Construction and Building Materials
Concrete canvas (CC) has good corrosion resistance and fire resistance, but it is rarely used in civil engineering. In this study, CC and carbon fiber-reinforced polymer (CFRP) are jointly used to reinforce concrete columns (i.e., jointly confined specimens) to expand their engineering application. To explore the axial compressive performance of combined CC-CFRP confinement concrete columns, 13 sets of specimens were designed in this study based on the number of CFRP layers, number of CC layers and volumetric stirrup ratio. The conclusions are as follows: 1) based on acoustic emission (AE) technology, the presence of CC can improve the uneven deformation of the concrete, and the jointly confined specimen has better energy dissipation capacity; 2) based on the experimental data, the peak stress of the jointly confined specimen is reduced by up to 10 % compared with the CFRP-confined specimen (i.e., the single confined specimen), and the ultimate strain is increased by at least 56.2 %, which shows that the jointly confined method is reasonable and feasible; and 3) the peak stress and ultimate strain models of the jointly confined specimen are obtained by numerical fitting, and a stiffness-based design-oriented compressive stress–strain model for the jointly confined specimen is proposed. Compared to existing models, the proposed model has higher accuracy, which can provide a theoretical basis for further research.
Alkali-activated slag mortar molded by non-stirring molding: Compressive strength, hydration properties and microstructures
2023, Case Studies in Construction Materials
Alkali-activated slag (AAS) characterized by fast hardening and high early strength has potential application prospects in concrete canvas (CC), where a non-stirring molding method is required to prepare mortar. This paper provides a new method for the preparation of alkali-activated slag mortar (AASM) by non-stirring (sprinkling-molding), where mechanical properties, hydration properties, and microstructures were investigated. The results suggest that the compressive strength of the sprinkling-molding mortar was slightly lower than that of the conventional stirring-molding mortar, and the compressive strength with sodium silicate content of 15 % the slag mass at 28d can reach 44.5 MPa. The hydration products are dominated by amorphous C-A-S-H gels, with small amounts of hydrotalcite. There are differences in degree of hydration and microstructures of each layer in the sprinkling-molding mortar.

View all citing articles on Scopus

View full text

Design and construction application of concrete canvas for slope protection

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Mechanical properties

Slope stability analysis

Conclusions

Acknowledgments

Constr. Build. Mater.

Powder Technol.

Powder Technol.

Geotext. Geomembr.

Comput. Geotech.

Comput. Geotech.

Cem. Concr. Res.

Constr. Build. Mater.

Compos. Struct.

Eng. Geol.

Comput. Geotech.

Eng. Geol.

Comput. Geotech.

Eng. Geol.