A Preliminary Research on Alkali-Activated Slag Concrete as Tunnel Lining in Severe Frigid Regions

2013 ◽  
Vol 668 ◽  
pp. 65-69 ◽  
Author(s):  
Heng Shu
Keyword(s):  
Frost Damage ◽  
Sem Analysis ◽  
Tunnel Lining ◽  
X Ray Diffraction ◽  
Alkali Activated Slag ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
Activated Slag ◽  
Alkali Activated

The main structure materials of tunnel lining are concrete and steel, and the concrete frost damage is a typical degradation phenomenon of the tunnel linings in cold regions. Alkali-activated slag concrete (ASC) has a better freeze-thaw resistance, which can be used for tunnel lining in severe frigid regions. Freeze-thaw resistance, performance mechanism of ASC and microstructure were investigated by freeze-thaw cycle, X-ray diffraction (XRD) and Scanning electron microscope (SEM) analysis. The experimental results show that, ASC has excellent freeze-thaw resistance, and hydration products of ASC are mostly C-S-H, alkaline aluminosilicate. ASC has a good compact degree and uniformity of structure, and its high compressive strength also makes high freeze-thaw resistance. ASC may be selected as tunnel lining production materials in severe frigid regions because of the less reduction in the dynamic elastic modulus and mass loss of concrete.

scholarly journals Experimental Study on the Durability of Alkali-Activated Slag Concrete after Freeze-Thaw Cycle

2021 ◽  
Vol 2021 ◽  
pp. 1-19
Author(s):  
Bin Chen ◽  
Jun Wang
Keyword(s):  
Compressive Strength ◽  
Elastic Modulus ◽  
Raw Material ◽  
Dynamic Elastic Modulus ◽  
Important Indicator ◽  
Alkali Activated Slag ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Activated Slag ◽  
Alkali Activated

A freeze-thaw resistance is an important indicator of the durability of alkali-activated slag concrete, which causes structural failure when the performance is low, especially in severely cold areas. In this study, solid sodium aluminate and sodium silicate were used as composite alkaline activators, while slag was used as the raw material to prepare alkali-activated slag concrete, whose freeze-thaw resistance, as well as that of ordinary cement concrete, was experimentally studied by varying the freeze-thaw cycles. The effects of the mass, compressive strength, and dynamic elastic modulus of the sample were investigated by considering the influence of different water-to-slag ratios and slag contents, while the damage variables and model were also analyzed. The results showed that alkali-activated slag concrete had an excellent freeze-thaw resistance, which was significantly affected by the water-to-slag ratio and compressive strength; specifically, the higher the water-to-slag ratio, the lower the freeze-thaw resistance, and the higher the compressive strength, the better the freeze-thaw resistance. The freeze-thaw durability, microstructure, and damage mechanism were studied via microscopic analysis. When analyzed via the microstructure test, crack pores and microcracks with narrow spaces and large surface areas were generated under freeze-thaw damage conditions, but the dense hydration structure and high-bonding-strength hydration products led to a better freeze-thaw resistance. The damage model was established using compressive strength and relative dynamic elastic modulus as damage variables, and the attenuation exponential and accumulative damage power function model had a high accuracy, which could better reflect the freeze-thaw damage law and damage degree and predict the lifetime of alkali-activated slag concrete.

Durability of Green High Performance Alkali-Activated Slag Pavement Concrete

2011 ◽  
Vol 99-100 ◽  
pp. 158-161 ◽  
Author(s):  
Yong Gen Wu ◽  
Liang Cai Cai ◽  
Ya Wei Fu
Keyword(s):  
Abrasion Resistance ◽  
High Performance ◽  
Mechanical Performance ◽  
Alkali Activated Slag ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
Activated Slag ◽  
Alkali Activated ◽  
Resistance Tests ◽  
Pavement Concrete

Green high performance alkali-activated slag pavement concrete(ASC) was prepared by adding Na2SiO3 and NaOH complex activator in slag. Physical, mechanical performance and durability of ASC were studied by workability, strength, hydrostatics and chlorin ion penetrability, fast freeze-thaw cycle tests and abrasion resistance tests. The results show that slump of ASC exceeds 160mm, fluidity and workability is excellent. 28d compressive and flexural trength of AAC are 91.9MPa and 8.5MPa, 7d compressive and flexural strength are 84.8MPa and 7.6MPa, which belongs to high–early strenth concrete. And its impermeability rank exceeds S40, chlorin ion impermeability is excellent, 6h eletricity is 1751～1894 coulomb, and its anti-frozen rank exceeds F300, which can meet the anti-frozen requirements in frore area. Depth of abrade slot is 0.45～0.96mm, abrasion resistance of ASC is 4.99, so its physical, mechanical performance and durability are superior to traditional portland concrete.

scholarly journals Study on the Progressive Deterioration of Tunnel Lining Structures in Cold Regions Experiencing Freeze–Thaw Cycles

2021 ◽  
Vol 11 (13) ◽  
pp. 5903
Author(s):  
Peng Xu ◽  
Yimin Wu ◽  
Le Huang ◽  
Kun Zhang
Keyword(s):  
Frost Damage ◽  
Tunnel Lining ◽  
Distribution Law ◽  
Cold Regions ◽  
Research Attention ◽  
Freeze Thaw ◽  
Progressive Deterioration ◽  
Structural Deterioration ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle

The linings of tunnels in cold regions with long service lives usually have cracks, with parts of the structure peeling and falling off, which seriously threatens the tunnel safety and operation. The unsaturated freeze–thaw cycle of concrete, which is the main cause of structural deterioration, has not received much research attention. During the service life of tunnels in cold regions, unsaturated freeze–thaw cycles deteriorate the quality of the concrete, and its degree presents a gradual distribution in the circumferential and longitudinal directions. An experiment system was adopted to simulate the distribution of the progressive deterioration of tunnel lining concrete. The test results of the temperature field of the model show the distribution law of freeze–thaw cycles, and the gradual deterioration of the lining concrete was realized. Then, the bearing capacity of the model was tested after the progressive deterioration. The results show that the ultimate load of the model decreases with an increase in the number of freeze–thaw cycles. Finally, a numerical simulation was carried out to discuss the influence of the gradual deterioration of the lining. The gradual deterioration of lining concrete will encourage the gradual development of cracks, leading to serious cracking of the lining structure and even block spalling. Through this study, we hope to provide useful information for the prevention and control of tunnel frost damage in cold regions.

scholarly journals The Effect of Freeze-Thaw Damage on Corrosion in Reinforced Concrete

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Xiao-Chun Lu ◽  
Bin Guan ◽  
Bo-Fu Chen ◽  
Xin Zhang ◽  
Bo-bo Xiong
Keyword(s):  
Reinforced Concrete ◽  
Corrosion Rate ◽  
Sem Analysis ◽  
Steel Reinforcement ◽  
Reinforcement Corrosion ◽  
Freeze Thaw ◽  
Pull Out ◽  
Thaw Cycle ◽  
Corrosion Reaction ◽  
Freeze Thaw Cycle

The existing studies of the corrosion of reinforced concrete have mainly focused on the interface area and chemical ion erosion, ignoring the specific service environment of the reinforced concrete. In this study, the effect of freeze-thaw damage was investigated via corrosion experiments under different freeze-thaw cycle conditions. Steel reinforcement corrosion mass, ultimate pull-out force, corrosion rate, and bond slippage were chosen as characteristic parameters in the experiments, and scanning electron microscopy (SEM) analysis was used to explain the mechanism of action of freeze-thaw damage on corrosion. The results showed that, under identical corrosion conditions, the mass of steel reinforcement corrosion and corrosion rate increased by 39.6% and 39.7% when comparing 200 freeze-thaw cycles to 0 cycles, respectively. The ultimate pull-out force and bond slippage after 200 freeze-thaw cycles decreased by 73% and 31%, respectively, compared with 0 freeze-thaw cycles. In addition, SEM analysis indicated that microstructure damage caused by freeze-thaw cycles accelerated the corrosion reaction and decreased cementitious properties, leading to decreasing ultimate pull-out force and bond slippage. The effect of freeze-thaw cycles and steel reinforcement corrosion on the macro mechanical properties of concrete is not a simple superposition.

scholarly journals Mitigating the Drying Shrinkage and Autogenous Shrinkage of Alkali-Activated Slag by NaAlO2

Materials ◽  
2020 ◽  
Vol 13 (16) ◽  
pp. 3499
Author(s):  
Bin Chen ◽  
Jun Wang ◽  
Jinyou Zhao
Keyword(s):  
Autogenous Shrinkage ◽  
Drying Shrinkage ◽  
Nitrogen Adsorption ◽  
Partial Substitution ◽  
Hydration Reaction ◽  
X Ray Diffraction ◽  
Na2o Content ◽  
Alkali Activated Slag ◽  
Activated Slag ◽  
Alkali Activated

The shrinkage of alkali-activated slag (AAS) is obviously higher than ordinary Portland cement, which limited its application in engineering. In this study, the effects of NaAlO2 in mitigating drying shrinkage and autogenous shrinkage of AAS were studied. To further understand the shrinkage mechanism, the hydration products and microstructures were studied by X-ray diffraction, scanning electron microscopy and nitrogen adsorption approaches. As the partial substitution rate of NaAlO2 for Na2SiO3 increased, the drying shrinkage and autogenous shrinkage reduced significantly. The addition of NaAlO2 could slow down the rate of hydration reaction and reduce the porosity, change the pore diameter and the composition of generated paste and cause more hydrotalcite and tetranatrolite generated—which contributed to reduced shrinkage. Additionally, raising the Na2O content rate caused obvious differences in drying shrinkage and autogenous shrinkage. As the Na2O content elevated, the drying shrinkage decreased and autogenous shrinkage increased. A high Na2O content would cause complete hydration reactions and provoke high autogenous shrinkage. However, incomplete hydration reactions left more water in the paste, and the evaporated water dramatically influenced drying shrinkage. The results indicate that addition of NaAlO2 could greatly mitigate the drying shrinkage and autogenous shrinkage of AAS.

scholarly journals The Durability of One-Part Alkali-Activated Slag-Based Mortars in Different Environments

2020 ◽  
Vol 12 (9) ◽  
pp. 3561 ◽  
Author(s):  
Luigi Coppola ◽  
Denny Coffetti ◽  
Elena Crotti ◽  
Gabriele Gazzaniga ◽  
Tommaso Pastore
Keyword(s):  
Magnesium Sulphate ◽  
Alkali Content ◽  
Freezing And Thawing ◽  
Alkali Activated Slag ◽  
Freeze Thaw ◽  
Gypsum Formation ◽  
Binder Ratio ◽  
Activated Slag ◽  
High Alkali ◽  
Alkali Activated

The paper assesses the durability of one-part alkali-activated slag-based mortars (AAS) in different aggressive environments, such as calcium chloride- and magnesium sulphate-rich solutions, in comparison with traditional cementitious mortars at equal water to binder ratio. Moreover, the freezing and thawing resistance was evaluated on mortars manufactured with and without air entraining admixture (AEA). Experimental results indicate that the alkali content is a key parameter for durability of AAS: the higher the alkali content, the higher the resistance in severe conditions. In particular, high-alkali content AAS mortars are characterized by freeze–thaw resistances similar to that of blast furnace cement-based mixtures, but lower than that of Portland cement-mortars while AAS with low activators dosages evidence a very limited resistance in cold environment. The effectiveness of AEA in enhancement of freeze–thaw resistance is confirmed also for AAS mortars. Moreover, AAS mixtures are quasi-immune to expansive calcium oxychloride formation in presence of CaCl2-based deicing salts, but they are very vulnerable to magnesium sulphate attack due to decalcification of C-S-H gel and gypsum formation.

scholarly journals Influence of Freeze-Thaw Cycles on Engineering Properties of Tonalite: Examples from China

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Su-Ran Wang ◽  
You-Liang Chen ◽  
Jing Ni ◽  
Mu-Dan Zhang ◽  
Heng Zhang
Keyword(s):  
Fracture Toughness ◽  
Young’S Modulus ◽  
Minimum Temperature ◽  
Young's Modulus ◽  
Physical And Mechanical Properties ◽  
Frost Damage ◽  
Engineering Properties ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle

The deterioration of the physical and mechanical properties of tonalites subjected to freeze-thaw cycling under three different temperature ranges was explored using several experimental techniques. Uniaxial compression and three-point bending tests were conducted on untreated and treated tonalite specimens. Clear decreases in uniaxial compressive strength (UCS), Young’s modulus, and fracture toughness were observed in tonalite specimens with frost damage. Although Young’s modulus and fracture toughness did not show clear decreases as the minimum temperature of the freeze-thaw cycle decreased from −30°C to −50°C, the UCS decreased almost linearly. The macromechanical characteristics of the tonalites can be explained by changes in mineral content and microstructure. The intensity of X-ray diffraction (XRD) peaks of minerals in tonalites that had not been freeze-thaw cycled were approximately 10 to 20 times higher than the peaks for the specimens subjected to freeze-thaw cycling, implying that the internal structure of tonalite is less compact after frost damage. The microstructures of the tonalite specimens were also examined using scanning electron microscopy (SEM). Increased amounts of fragmentation and breaking of structural planes were observed as the minimum temperature of the freeze-thaw cycle decreased.

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