Evaluation of Tensile Strength of Different Mortar and Adhesive Specimens Used in Masonry Wall Construction

*Yağmur Kopraman, Coşkun Çakmak and Anıl Özdemir* 

#### **Abstract**

In recent years, experimental study on non-load-bearing walls has been incremented. In the light of these studies, knowledge on the mechanical properties of construction materials used as binders is rapidly growing. Prior to wall construction, different kinds of binding materials could be chosen with respect to usage objectives and availability. In this study, the most widely used construction materials, namely, cement-lime mortar, gypsum mortar, and specially designed chemical brick adhesive, were chosen. Cylinder specimens using the mentioned construction materials were tested to evaluate their tensile strength. For each type of construction material, three identical specimens were produced. This experimental study is compiled from the data collected from a total of nine specimens. Tests were done according to ASTM standard C496-17 standard. During the tests, vertical displacement, vertical and horizontal strain readings, and applied load readings were collected. As a result, whatever the material was, all has yielded approximately the same tensile strength.

**Keywords:** masonry wall, mortar, adhesive, tensile strength, Brazilian test

#### **1. Introduction**

Non-load-bearing walls are widely used in every structure as partition walls. In general, natural stone, clay brick unit, aerated concrete brick unit, lightweight concrete brick unit, or even concrete blocks are widely used as wall construction materials. The variety of available materials allow constructors to choose the most suitable one according to economy, usage needs, insulation demand due to heat and sound, and finally local availability [1]. On the market, each individual wall unit is bound to each other with some kind of specific binder or mortar. Randomly chosen binder may not satisfy needed workability and usage objectives.

 Most of the unit to unit binders used in non-load-bearing walls consist of certain amounts of fine-graded materials and water, mixed to form a workable putty within a decent amount of time [2]. In this study, the most widely used construction materials were chosen which are concrete lime mortar, gypsum mortar, and specially designed chemical adhesive. This experimental study is the completed portion of a large unfinished experiment, aimed to investigate the computer simulation of non-load-bearing partition walls.

#### **2. Literature survey**

There are various methods of testing stone or brittle materials in tension [3–7]. The most common method of tensile testing is bending tests either by three- or four-point loading of unreinforced beam specimens [8]. Although the test procedure is quite easy, these testing methods are used to yield twice the strength compared to calculations done by Hooke's law [9].

 Hübert Rüsch in the 1960s designed a prism-shaped specimen tested in pure tension. But, local failures were observed where the loading apparatuses contact with the specimen. So Rüsch increased the cross section of the specimen where contacts lead to a local failure. The test method which gives the closest result to the actual tensile strength of the test specimens is"Simple Tensile Test" [10]. Although this method is known to output the real-life tensile strength, the specimen preparation and its placement in the test setup need more effort, and repeatability of test procedure is quite low [11].

 Another technique used for determining tensile strength of brittle materials is first introduced by Carneiro and Barcellos in 1953. This technique is named as *cylinder split test* or *Brazilian test* [12]. The Brazilian test, accepted as standardized test method, included the major international standards such as ASTM C496, ISO 4105, BS 1881-117, and RILEM CPC6 [13–16]. In recent years, Brazilian test is more widely used than bending tests for determining specimen tensile strength, for its low error rate and much standardized output in the test results. Therefore, in this study Brazilian test procedure was used to determine the tensile strength. For this purpose, cylindrical specimens having standard dimensions, 150 mm in radius and 300 mm in length, was placed horizontally in a compressive testing machine. Compressive load transfer is applied to the test specimen, with a pair loading apparatus made up of hardboard having width, length, and thickness of 10, 300, and 5 mm, respectively. Loading apparatuses were located at 12 and 6 o'clock position, respectively, where the cylindrical specimen touches the compressive testing machine. Thus, concentrated linear compressive stress was applied that leads to an elongation in the perpendicular direction where the deformation is unconstrained. As a result, a crack pattern occurs along the 12–6 o'clock direction which causes the specimen to split into two identical halves. This brittle failure mechanism, reveals that as the specimens get wider and longer, much more compressive load is needed to crush the specimen [17, 18]. Therefore, the dimensions and the rate of loading of all the specimens in this experimental study are kept identical. And to overcome material defects, each test is repeated three times.

A basic scheme of Brazilian test setup and the stress distribution along cracked specimen was shown in **Figure 1**.

**Figure 1.**  *Cylinder splitting tensile strength test [19].* 

*Evaluation of Tensile Strength of Different Mortar and Adhesive Specimens Used in Masonry… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

It should be noted that, apart from the outer edges where some local crushing is observed, uniform tensile stress distribution develops at the inner layers of the specimen. For that reason, this method of testing yields dependable and trustworthy results. ASTM standard C496-17 [20] proposes Eq. (1) to be utilized while calculating the shear stress on specimens:

$$
\sigma = \frac{2\text{ P}}{\pi \text{ D L}} \tag{1}
$$

where:

σ is the splitting tensile strength, MPa.

P is the maximum applied load indicated by the testing machine, N.

L is the length of the specimen, mm.

D is the diameter of the specimen, mm.

 In **Table 1**, the proposed equations of available tensile test methods used for tensile capacity prediction of concrete in terms of compressive strength were shown [9]. The direct tension test being the most ideal method, the closest value was proposed by Brazilian test.


**Table 1.** 

*Tensile strength of concrete by various test methods.* 

#### **3. Experimental study**

 Test specimens were produced and tested in the structural mechanics' laboratory of the civil engineering department in Gazi University. Specimens were cast by the layers approximately each having 100 mm. Each layer of material was carefully placed in the pot leaving no gaps or voids. For each construction material, three identical shaped specimens were taken. Each type of construction material stayed in the pot for 2 days and then was taken out. Drying process lasted for 4 weeks. At the day of testing, all specimens had a similar aging process, which lasted between 30 and 32 days at a controlled ambient temperature level of 20°C (68°F). No additional care or cure process was utilized during production. Concrete-lime mortar was prepared by mixing cement, lime, 0–3 mm graded sand, and water by the volumetric ratios of 1, 1, 4, and 1, respectively. Gypsum and chemical wall unit adhesive needed only water to be added into the dry content. For gypsum mortar preparation, 4 volumetric units of dry gypsum powder were mixed by 3 volumetric units of water. The mix design of chemical wall unit adhesive consisted of water and dry content, which was expressed as 0.59–1 volumetric ratio, respectively. For all construction material types, each individual mixing speed and duration were applied carefully. Experiment elements were shown on **Figure 2**.

 In **Figure 3**, test and loading setup was shown. Specimens were tested in a custommade axial load test frame having 3000 kN of loading capacity. The load was applied at a rate of 3 kN/s with a computer-controlled hydraulic jack. During the test five sensor readings were taken simultaneously. Readings were collected through a digital data logger device which collects eight readings per second. Two vertical direction

**Figure 2.**  *Production of test specimens.* 

**Figure 3.** 

*Testing and measuring instrument setup.* 

 linear displacement readings, two strain gauge (SG) readings at vertical and horizontal directions, and applied axial load were collected throughout the experiments. Although the strain gauge readings were planned as the dominant deformation reading, during tests after the development of shear cracks, vertical strain stopped responding. Besides, horizontally placed strain gauge transmits no meaningful strain reading if the crack was missed. So as a backup, mathematical average of the linear displacement readings was used to verify the vertical strain gauge reading. But in the horizontal direction, very delicate strain gauges are damaged suddenly after the first observable crack, and rapidly growing crack leads gauges to lose its consistent data output. For this reason, especially, horizontally placed strain gauges mostly failed to inform dependable readings. For that reason, the selected horizontal strain plot of only one specimen was given. Others were omitted because of sudden loss or misplaced gauge. **Figures 4–6** show experiment elements before the tests.

Tensile stress-strain graphs were plotted by using the data of experimental phase, and the behavior of the binding materials against the applied load was determined. The experimental observation and stress-strain graph of nine test specimens (three concrete-lime mortars, three gypsum mortars, three chemical adhesives) will be presented in the following section.

*Evaluation of Tensile Strength of Different Mortar and Adhesive Specimens Used in Masonry… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

**Figure 4.**  *View of concrete-lime mortar specimens prior to testing.* 

**Figure 5.**  *View of gypsum mortar specimens prior to testing.* 

**Figure 6.**  *View of chemical adhesive specimens prior to testing.* 

### **4. Experimental results**

 As aforementioned nine Brazilian tests were carried out for three different kinds of binders. Tensile strength of each mortar type was obtained by averaging the three test results. Compiled test results are shown in **Table 2**. The average of gypsum and cement-lime mortar specimens crushed approximately at the same level of tensile stress. The tensile strength of the adhesive mortar was about 15% lower than the other mortar types. Graphs plotted using the calculated stress-strain values were presented in **Figures 7**–**9**. Three tests were carried out for every kind of mortar, but just in first tests, strain gauges were utilized to be able to define the relation of


#### **Table 2.**

*Test results.* 

**Figure 7.**  *Tensile strength and strains in vertical and lateral direction of gypsum mortar specimens.* 

 vertical and horizontal strain magnitude values. The other two tests were carried out to confirm the tensile strength of specimens. It is clear to see, from the first figures of every triple figure set, how vertical strain of the specimen changes versus its lateral strain value under the effect of the same load magnitude. For example, the first graph in **Figure 7** shows that vertical strain of the gypsum mortar specimen 1 is equal to nearly three times its lateral strain value under the effect of the same load magnitude. In addition, final shapes after the failure of mortars were shown in **Figures 10**–**12**.

#### **4.1 Gypsum mortars**

From the outcome of first test, it is possible to conclude that until 0.005 mm/mm strain in both directions moved closely to each other. After this value, vertical strain moved faster than the lateral one. Gypsum mortar specimen had tensile strength of 0.16 MPa in average. All specimens reached their tensile strength value at relatively 0.06 mm/mm, vertical strain value. Even though strength results are different from

*Evaluation of Tensile Strength of Different Mortar and Adhesive Specimens Used in Masonry… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

**Figure 8.** 

*Tensile strength and strains in vertical and lateral direction of cement-lime mortar specimens.* 

**Figure 9.**  *Tensile strength and strains in vertical and lateral direction of chemical adhesive mortar specimens.* 

**Figure 10.**  *View of concrete-lime mortar specimens after test.* 

**Figure 11.**  *View of gypsum mortar specimens after test.* 

**Figure 12.**  *View of chemical adhesive specimens after test.* 

each other, behavior of specimens was nearly similar. Specimens kept their bearing load until they reach about 0.05 mm/mm vertical strain value in three tests. In addition, the strain interval, from beginning to increase of bearing load to reach their maximum bearing load, is 0.01 mm/mm, and it is again nearly the same for each specimen.

#### **4.2 Cement-lime mortars**

Data obtained indicate that in scope of strain and strength, behaviors of cement mortar specimens are quite similar to gypsum mortar specimens. Cement mortar specimen had tensile strength value of 0.15 MPa in average. They reached to this level of stress averagely at 0.06 mm/mm vertical strain value.

#### **4.3 Chemical adhesive mortars**

This test set showed that strain behaviors of three different tests arose disparately. In the first test, as soon as the test started, the bearing load increased without showing any behavior like keeping the same load-bearing capacity. In the second and third test, although the strength and strain values are different, they are similar to other types of mortar in terms of failure behavior. Adhesive mortar specimens had tensile strength values relatively 0.12, 0.13, and 0.15 MPa. They reached their tensile strength value at relatively 0.03, 0.05, and 0.08 mm/mm vertical strain values.

*Evaluation of Tensile Strength of Different Mortar and Adhesive Specimens Used in Masonry… DOI: http://dx.doi.org/10.5772/intechopen.87836* 

#### **5. Conclusion**

 In this study tensile strength of the most widely used mortar types was calculated and compared to each other by Brazilian test method. This study is a subgroup of a project, which is about investigating earthquake performance of partition wall systems of which experimental studies were already done. An analytical study is also being planned about this topic to be able to confirm the results. For this analytical study, mechanical properties of every component that constitutes these wall systems should be calculated in order to transfer the material properties to the computer. Because mortars are the most important connectors for masonry units to each other, it is significant to define their mechanical properties too. For this reason, the main limitation of the experimental study is just to define tensile strength of mortar specimens that are most widely used in construction sector. In addition, there was a lack of mechanical behaviors of mortar types in academic literature. Based on the results, it can be concluded that mortar types have close tensile strength values. Additionally, for all kinds of mortars, failure in shape was very brittle and stress accumulation occurred in the same regions. It is recommended that these tests can be carried out with a high number of specimens and maybe with different components like cement/water or gypsum/water ratios.

#### **Acknowledgements**

The authors would like to acknowledge the support from the Gazi University-Projects of Scientific Investigation (BAP)(Research ID: 07/2018–2102).

#### **Author details**

Yağmur Kopraman, Coşkun Çakmak and Anıl Özdemir\* Department of Civil Engineering, Gazi University, Ankara, Turkey

\*Address all correspondence to: anilozdemir@gazi.edu.tr

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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**709**

**Chapter 57**

**Abstract**

soil liquefaction, BNWF

**1. Introduction**

The Effect of Pile-Head Boundary

The soil may lose its strength due to various reasons. Especially in saturated sandy soils, because of the increase in pore water pressure under dynamic loads, the soil loses its strength and behaves as a liquid. Liquefaction phenomenon, along with the occurrence of large soil displacements, can cause lateral spreading in sloping ground. These displacements cause some damage on pile foundations. It is still hard to determine the behavior of laterally loaded piles under dynamic loading with definite judgments. For this reason, some numerical and experimental methods are used. In this study, some centrifuge test results are compared with those obtained numerically with a beam on nonlinear Winkler foundation (BNWF) model.

The increase of pore water pressure during an earthquake triggers the liquefaction phenomenon, which in turn in the case of sloping ground conditions may trigger the lateral spreading phenomenon. Lateral spreading due to soil liquefaction in steep slopes causes the soil to lose its stiffness by being exposed to large lateral displacements. Both lateral spreading and liquefaction phenomenon occur due to the reduction of strength and stiffness of the soil. Therefore, in case of soil liquefaction and lateral spreading, large stresses may occur on pile foundation, resulting in considerable damage to the pile. In Turkey and in other countries severely exposed to large earthquakes, many studies have been carried out on pile damages due to liquefaction and lateral spreading, and their effects on the superstructure behavior have been evaluated. The 1964 Niigata (Mw = 7.5), 1964 Alaska (Mw = 9.2), 1971 San Fernando (Mw = 6.4), and 1995 Hyogoken-Nambu (Mw = 7.2) earthquakes caused liquefaction and lateral spreading and in literature is reported that piles damage due to these phenomena occurred. A semi-analytical analysis method was presented in [1] to capture the dynamic response of vertical floating pile groups. Numerical results suggested that this method gave better results than the finite element method [1]. In the past, the behavior of piles under seismic loads was studied with numerical methods (i.e., p-y curves and finite element method) [2], and the results obtained were compared with centrifuge test experimental data [3–6]. Other researchers have performed centrifuge tests to better understand the performance, in a liquefiable deposit, of piles beneath the bridge piers and then have attempted to reproduce these tests with the help of numerical tools based on the finite difference

Conditions in Liquefiable Soil

*Pınar Sezin Öztürk Kardoğan and Nihat Sinan Işık*

**Keywords:** pile, pile-soil interaction, pile-head boundary conditions,

#### **Chapter 57**
