Introduction
This increase in solid waste generation is due to growing population and consumption patterns. Unused ash in the form of fly ash is typically disposed of in open ponds, forests, and open lands (AACPA, 2017).
Autoclaved Aerated Concrete (AAC) Block
A brief introduction, advantages, disadvantages, applications and fabrication process of AAC are discussed in further sub-sections. However, it was produced in the northeastern part of the country in 2014 and opened for commercialization in 2015.
Application of AAC
For example, Costa et al. 2011) have investigated the Seismic Performance of AAC masonry using both experiments and simulations. According to the findings of Costa et al. 2011), unreinforced CAA masonry can withstand low to moderate seismic events when the building geometry is regular.
Advantages and Limitations of AAC
With a high porosity, thereby low density (~500 kg/m3) and thermal conductivity (0.1 W/(mK)), the AAC material can serve as a soundproofing and thermal insulation material. The AAC material breaks down easily; the face of the block is easily damaged during the scaffolding.
Manufacturing Process of AAC
- Mixing of raw materials
- Pouring of final mix
- Expansion of the mix slurry
- Wire cutting of cake
- Autoclaving or hydrothermal treatment
After the demoulding process, the big green cake is transferred to the wire cutting line. During the horizontal cutting, the large green cake is fed through the arrangement of 5 wires equipped in horizontal cutting machine.
Scope of the Present Thesis
After autoclaving, the hardened or hardened stack of AAC blocks is pulled out of the autoclave chamber using a ferry cart. Finally, the completed AAC blocks are taken to the warehouse with the help of a forklift.
Organization of the Thesis
Therefore, for this purpose, a layer of cement was used on the face of the AAC bed to increase the bond strength of the block-mortar interface. In this chapter, a method of improving the bond strength (both tensile and shear) of ordinary sand-cement mortar without changing the surface characteristics of the block is proposed.
Introduction
Physical Properties of Autoclaved Aerated Concrete (AAC)
- Density
- Moisture content, water absorption and initial rate of absorption
The density is mainly controlled by the dose of aluminum powder in the raw material mixture during the production of AAC in the plant (Kunchariyakun et al. The average moisture content of the AAC blocks lies in the range of 2–18% of the sample weight (Bhosale et al . 2019).
Strength of Individual AAC Unit
- Compressive strength of AAC unit
- Modulus of elasticity of AAC unit
- Tensile strength of AAC unit
The water to solid (W/S) ratio is a critical criterion for adjusting the compressive strength of AAC. The compressive strength of AAC is relatively low compared to conventional brick/block used in building construction.
Mechanical Properties of AAC Masonry
- Compressive strength of AAC masonry
- Shear bond strength of AAC masonry
- Tensile bond strength of AAC masonry
The shear strength of masonry increases as the moisture content in the brick increases (Sinha 1983). The shear strength of masonry increases with the increase in the compressive strength of mortar (Rahman and Anand 1994 and Malikarjuna 2017).
Finite Element (FE) Modeling of Masonry Strength
- Concrete damage plasticity (CDP) for material modeling
- Cohesive Zone Modeling
2.9) where τt is the tensile bond strength, (Pt)max is the maximum value of the applied load and A. The average tensile bond strength and the corresponding mode I fracture energy were found to be 0.056 MPa and 0.01 N/mm , respectively. The shear strength or bond strength of masonry depends mainly on the interface between the unit and the mortar.
Major Gaps in the Literature
It was concluded that the simplified micromodeling is a convenient method for finite element modeling of the masonry shear wall. The stiffness of the wall mainly depends on the bond strength between brick and mortar and not on the strength of the mortar (Mallikarjuna 2017). Despite this, the influence of mortar or adhesive thickness on the overall strength of AAC.
Detailed Objectives of the Present Thesis
The third objective of this thesis investigates the bond strength of AAC block-mortar interface made of ordinary sand-cement mortar of different compositions and polymer modified mortars. A method is proposed to improve the bond strength (both tensile and shear) of ordinary sand-cement mortar without changing the properties of the block surface. The developed model has been used for the estimation of the compressive strength of AAC masonry.
- Introduction
- Machines used for testing the strength of AAC masonry
- Universal testing machine (UTM)
- Servo hydraulic actuator
- Laser extensometer
- Experimental Setup for Strength Test of AAC and its Masonry
- Experiment setup for compression test of AAC block
- Experiment setup for tensile test of AAC block
- Experiment setup for compression test of AAC masonry
- Experiment setup for shear bond strength test of AAC masonry
- Experiment setup for tensile bond strength test of AAC masonry
- Conclusions
In this study, a computerized UTM of capacity 1000 kN (Model: TUE-C-1000), as shown in Figure 3.1, was used to estimate the compressive strength of AAC block and its masonry. A servo-hydraulic actuator was used to perform the tests for evaluating shear bond strength and tensile bond strength of AAC specimen. The tensile strength of AAC cylindrical specimen was calculated using the theory of isotropic elasticity.
- Introduction
- Materials and Specimen Preparations
- Test for physical properties of AAC block
- Test of compressive and tensile strengths of AAC blocks
- Test for compressive strength of mortars
- Test for compressive and bond strengths of AAC masonry
- Results and Discussion
- Compressive and tensile strengths of AAC block
- Compressive strength of AAC masonry
- Conclusions
The results of the test are summarized in Table 4.3; the compressive strength of AAC masonry prism increases with an increase in the compressive strength of the mortar. The masonry tensile strength results for various mortars are in the MPa range. The use of M1 mortar changes the failure pattern, i.e. the block will fail before the failure of mortar.
Introduction
Moreover, in the next chapter (Chapter 6) the improvement of the bond strength with fresh cement slurry coating is studied. This chapter reports rigorous experiments on the sliding shear connection (along the joint) and compressive strength of grooved AAC masonry.
Concept of Grooved AAC Block
Finally, hardened AAC blocks as well as grooved blocks were obtained after 18 hours of autoclaving. The picture of the various stages for the production of AAC grooved blocks using miniature is shown in Figure 5.2. All stages (pouring, raising, cutting and autoclaving) in the production of grooved AAC block using the miniature mold were carried out in an industry, producing conventional AAC blocks following the usual industrial practice as discussed in Chapter 1.
Testing Methods and Specimen Preparation
- Determination of compressive strength of AAC block
- Determination of shear bond strength of block-mortar interface
- Determination of compressive strength of AAC masonry
The shear strength of the block mortar joints (without pre-compression) was studied by testing the AAC block triplets. The load and boundary conditions for different types of AAC masonry during the shear adhesion test are shown in Figure 5.5. The compressive strength of the masonry was evaluated according to the peak load at failure during the test.
Simplified Models for the Determination of Load Carrying Capacity of Grooved
For example, for a double-groove block (DGB) the load carrying capacity is given by. 5.3) Similar equations can be developed for blocks with more than two grooves. The mathematical model for determining the shear load carrying capacity of a masonry triple has also been developed along similar lines. Once and c are known, the shear load carrying capacity of a multi-groove masonry trio can be estimated.
Hypothesis Testing
The level of significance is the probability with which a hypothesis is rejected even if it is true. The value of t is compared with the value of tα, obtained from the statistical table corresponding to the level of significance (α). In this study, a hypothesis test was used to evaluate the level of significance of the experimental results for the compressive strength of blocks, as well as for the shear bond and compressive strength of AAC masonry.
Results and Discussion
- Compressive load carrying capacity of AAC blocks
- Shear load carrying capacity of AAC masonry triplet
- Compressive load carrying capacity of AAC masonry prism
- Hypothesis testing of experimental results
The lower and upper estimates of the pressure bearing capacity of the DGB block (from equation 5.3) are given by (PMSGB)min and (PMSGB)max are the lower and upper estimates of the pressure bearing capacity of SGB masonry prisms. The lower and upper estimates of pressure-bearing capacity of DGB masonry prism (from equation 5.25) are given by.
Conclusions
The percentage increase in compressive strengths of DGB and SGB masonry over PB masonry is found to be 9.6% and 4% respectively. Thus, the findings of this work strongly support the improvement of shear load carrying capacity of a masonry using grooved AAC blocks; however, no strong claim can be made for improving compressive strength.
Introduction
Although the compressive strength of the masonry increases with decreasing joint thickness (Sarangapani et al. Compared to studies on the bond strength of clay bricks and cement-soil blocks, there are very few studies available in the case of AAK masonry. The effect of joint strength on the overall performance of AAK masonry has not been investigated.
Materials used in the Study
- Autoclaved aerated concrete (AAC) blocks
- Joint materials
In fact, one randomly selected AAC block from the same industry provided an average compressive strength of 3.23 MPa. The compressive strength test of the PMM mortar sample was performed after 28 days of curing in water and then 3 days of drying. It should be noted that the compressive strength of PMM mortar is 6 MPa lower than that of SCM3 mortar, the weakest sand-cement mortar in this study.
Specimen Preparation and Testing Methods
A photograph and front elevation drawing of the triplet test setup is shown in Figure 3.7. The shear bond strength was calculated corresponding to the peak load during the test. Loads acting on the block and the free-body diagram of the center block are shown in Figure 6.2. The tensile bond strength was calculated corresponding to the peak load at the fracture divided by block-mortar interface contact area.
Results and Discussion
- Shear bond strength of the masonry triplet
- Tensile bond strength of the cross-couplet specimen
- Comparison of observed bond strength of masonry employing various joining
- Cost comparison
A failure in gluing is a breakdown of the interfacial bond between the adhesive (block) and the glue (mortar). The shear strength of the CSCM3 joint is significantly higher than that of ordinary sand-cement mortar. The tensile strength of the joint for all types of mortars is in the MPa range. The failure patterns during the tensile strength test of the cross-joint specimens are shown in Figure 6.6.
Conclusions
Introduction
Although several researchers have studied the numerical modeling of AAC masonry strength such as compressive strength and bond strength, none have modeled the development of lateral stresses corresponding to the applied axial compressive load. The purpose of this chapter is to present finite element modeling of AAK masonry under compressive load. The behavior of AAK masonry subjected to uniaxial compressive loading is discussed in this section.
Finite Element Modeling of AAC Masonry Compressive Strength Using ABAQUS
The properties were experimentally evaluated based on the compressive strength test results of AAC blocks and mortar. The lateral displacement and thus the Gif's ratio of AAC block and mortar was evaluated using laser extensometer (Make: Epsilon; Model: LE-15). In the experiment, the compressive strength of AAC masonry was evaluated using the same 1:4 (cement: sand) grade mortar.
Conclusions
As can be seen in Figure 3 (b), which shows the lateral stress developed in the x-direction for an axial vertical load of 65 kN (z-direction), the lateral compressive stress is developed in the block part, while the lateral tensile stress is developed in mortar layers. A similar nature of lateral stress distribution for block and mortar was found in the y direction as for the x direction.
Introduction
For this, a grooved AAC block has been studied to increase the shear bond strength of AAC masonry. Increasing the bond strength of AAC masonry using the combination of cement slurry coating and conventional sand-cement mortar is another aspect of novelty/innovation in this research work. The thesis also reports the compressive behavior of AAC masonry using the finite element (FE) modeling method.
Evaluation of Mechanical Properties of Autoclaved Aerated Concrete (AAC) Block
The salient findings of the various subparts of the present work are summarized in the following sections.
Compressive and Shear Bond Strengths of Grooved AAC Block and its Masonry124
Subsequently, the bond strength of AAC block-mortar interface made from ordinary sand-cement mortar of different compositions and polymer-modified mortars was investigated. The shear and tensile bond strength of the masonry was investigated for all types of interfaces. Considering bond strength as well as cost, the use of a weak mortar (lean cement content) along with cement slurry coating was found to be superior to plain sand cement mortar and polymer modified mortar.
Finite Element (FE) Modeling of AAC Masonry for the assessment and analysis of
Overall Conclusion
Since current AAC blocks are smooth on all six surfaces, the shear strength of AAC masonry is low regardless of mortar type. Increasing the bond strength of AAC masonry using the combination of cement slurry coating and ordinary sand-cement mortar is also another aspect of novelty/innovation in this research work. The use of a combination of lean cement mortar and cement slurry coating, namely CSCM3, was found to be the best choice in terms of bond strength (both tensile and shear strength) and economy.
Scope for Future Work
Mechanical characterization of autoclaved air-entrained concrete masonry subjected to in-plane loading: Experimental investigation and FE modeling. Properties of autoclaved aerated concrete incorporating rice husk ash as partial replacement for fine aggregate. Previous and current investigations on the components, microstructure and main properties of autoclaved aerated concrete – A review.
