Thin Layer Mortar Research Articles

Influence of material properties on the modulus of elasticity of AAC masonry

AbstractAimThe goal of the presented study is to evaluate the influence of material properties on the modulus of elasticity of autoclaved aerated concrete masonry. In addition, it was assessed the reliability of the KE value included in the Eurocode 6 to calculate the modulus of elasticity of AAC masonry in relation to its characteristic compressive strength.MethodAn experimental campaign for the determination of modulus of elasticity of AAC masonry with a characteristic compressive strength in the range of 1.3‐2.0 MPa, was carried out. AAC units from different plants in Europe have been tested as well as the thin layer mortar used for the samples. The values of bulk density range between 270 and 350 kg/m3. Moreover, the testing comprised the determination of compressive strength as well as modulus of elasticity of masonry erected by using these blocks. Basis for testing of the compressive strength and modulus of elasticity was EN 1052‐1.ResultsThe experimental results were compared with the values of modulus of elasticity E calculated according to EN 1996‐1‐1. The comparison shows how the current range of values of KE reported by the German annex DIN EN 1996‐1‐1/NA fits well to the experimental results obtained.

Experimental investigation of negative temperature’s influence during block laying on mechanical properties of calcium silicate block masonry

This research analyzed the use of hollow masonry blocks made from calcium silicate, which were bonded using thin-layer and general purpose mortars. In particular, this article examines how low and negative environmental temperatures affect the mechanical properties of masonry during the process of block laying. Experimental research focuses on two stages of hardening, the first being the mechanical properties of masonry immediately after the mortar thaws in the joints. The second stage in our research examined the mechanical properties of masonry when warming mortar continues to harden. Performed research have shown that block laying at low temperatures affects both the compressive strength and the modulus of elasticity of masonry. Depending on the type of mortar used, the aforementioned modulus decreases to 15%, which has a direct impact on the load-bearing capacity of vertically loaded masonry constructions. This study shows that thin-layer mortar used in the laying of calcium silicate hollow blocks exhibits greater vertical deformations at the initial loading stage.

Research of Influence of the Shape of Unreinforced Masonry Shear Walls Made of Calcium Silicate Masonry Units

We performed tests on 6 calcium silicate masonry units which were laid in thin layer mortar with uneven head joints. Walls were divided into two series and denoted by convention as HOS (Jasiński 2016) and HOS-H. Those two series differed in overall dimensions of test elements. Three walls from HOS series had identical external dimensions: l = 4.50 m, h = 2.45 m (h/l = 2.45m/4.50m), and thickness t = 180 mm. The walls were tested at different values of initial compressive stress σc = 0; 0.1; 1.0 and 1.5 N/mm2. The HOS-H elements were prepared as unreinforced test elements with the length l = 2.25 m height h = 2.45 m (h/l = 2.45m/2.25 m) and thickness t=0.18 m, and tested at initial compressive stress equal to σc = 0.1; 0.75; 1.5 N/mm2. The tests showed that the wall shape had a negligible effect on the morphology of cracks and the failure mechanism. An increase in wall length caused a roughly proportional increase in values of cracking and failure stresses. Shorter walls were under considerably greater cracking and failure stresses. An increase in wall length led to a significant decrease in values of shear strain angle regardless of initial compressive stress. The reverse situation occurred at the moment of destruction. Values of shear strain then increased with an increasing length of the wall.

Experimental investigation of the bed joint influence on mechanical properties of hollow calcium silicate block masonry

The article discusses the influence of the bed joint thickness and mortar strength on properties of calcium silicate (CS) block behavior under short-term static load. The investigation of masonry samples made of hollow CS blocks is presented in this paper. The specimens were made of two types of hollow CS blocks, combined with general purpose mortar of three different strengths and thin layer mortar of two different strengths. During the analysis of masonry with thin layer mortar the moisture influence on mechanical properties of masonry was also investigated. The experimental investigation has shown that the height of mortar bed joints has a larger influence on the mechanical properties of masonry when mortar of lower strength is used. Moistening CS blocks with thin layer mortar did not have a significant influence on the mechanical properties of masonry.

Limitation of cracking in AAC masonry under the window zone

AbstractThe article describes the results of tests on the impact of reinforcement on the appearance of cracks and on the manner of damage to masonry under the window zone. Masonry made of Autoclaved Aerated Concrete units with thin layer mortar was tested. Eight unreinforced test specimens (two series) and four series of test specimens (12 specimens) with reinforcement in the bed joints were subject to testing. Two types of reinforcement were used in the tests. It is demonstrated that the reinforcement has a significant impact on the level of cracking stress and propagation of cracks. It was found that when a pillar is correctly designed, cracks should not occur in the masonry under the window zone.

Properties of Different Mortars and their Effect on the Flexural Strength of Low Density Block Walls

Mortar for masonry is important because it provides the linkage between masonry units so enabling the composite to behave as a single material. The type of mortar used determines the flexural and compressive strength of the masonry so in this paper, a range of mortars are examined and their effects on the flexural strength of low density block walls determined. These include traditional designation (iii) (1 cement : 1 lime : 6 sand), designation (iv) (1 cement : 1 lime : 9 sand) mortars as defined in BS 5628, and two thin layer mortars. The conventional mortars were formed using both 42.5N or 32.5N PC to BS EN 197 in order to ascertain the difference these two cements have on the properties of mortar. The thin layer mortars show remarkably high compressive strength. The characteristic flexural strength of low density aircrete wallettes incorporating both these conventional and thin layer mortars was verified. The wallettes were tested in accordance with British and European standards. The flexural strength of aircrete wallettes was derived from the strength of small specimens tested to destruction under four-point loading. The strengths of the wallettes are high with impressive repeatability with the maximum strength being reached for thin layer wallettes within 7 days curing time. In general the strengths of both conventional mortar and thin layer mortar wallettes compare favourably to values reported in the standards.

Properties of Different Mortars and their Effect on the Flexural Strength of Low Density Block Walls

Mortar for masonry is important because it provides the linkage between masonry units so enabling the composite to behave as a single material. The type of mortar used determines the flexural and compressive strength of the masonry so in this paper, a range of mortars are examined and their effects on the flexural strength of low density block walls determined. These include traditional designation (iii) (1 cement : 1 lime : 6 sand), designation (iv) (1 cement : 1 lime : 9 sand) mortars as defined in BS 5628, and two thin layer mortars. The conventional mortars were formed using both 42.5N or 32.5N PC to BS EN 197 in order to ascertain the difference these two cements have on the properties of mortar. The thin layer mortars show remarkably high compressive strength. The characteristic flexural strength of low density aircrete wallettes incorporating both these conventional and thin layer mortars was verified. The wallettes were tested in accordance with British and European standards. The flexural strength of aircrete wallettes was derived from the strength of small specimens tested to destruction under four-point loading. The strengths of the wallettes are high with impressive repeatability with the maximum strength being reached for thin layer wallettes within 7 days curing time. In general the strengths of both conventional mortar and thin layer mortar wallettes compare favourably to values reported in the standards.

Field testing the strength of thin-layer mortars using the pull-out method

Reinforced steel bar (rebar) mesh and thin-layer mortar are applied to reinforce sintered clay brick walls in a construction site. Their strengths are measured using the pre-installed pull-out method, the post-installed pull-out method and the standard cube compression strength test. Nine strength grades of cement mortars, namely, M10, M15, M20, M25, M30, M35, M40, M45 and M50, are chosen for the test; the pre-installed and post-installed pull-out tests consist of 54 samples of each. By fitting the experimental results, a formula for the compressive strength of the thin-layer mortar for the pre-installed and post-installed pull-out tests is developed. The regression function is validated and an interval prediction of the specific compressive strength for the pre-installed pull-out test is proposed. This study provides a basis for wider application of the pull-out test for thin-layer mortar and the establishment of its technical standards.

Experimental assessment of the in-plane lateral capacity of autoclaved aerated concrete (AAC) masonry walls with flat-truss bed-joint reinforcement

Experimental campaigns carried out in the past showed that the presence of truss bed-joint reinforcement provides a general improvement to the performance of masonry panels subjected to horizontal actions. The truss-like elements are effective in improving resistance and reducing damage and, therefore, they enhance the displacement capacity. The experimental tests available in the literature, performed on prototypes in different scale or in small number compared to the possible combinations of slenderness, axial load and boundary conditions, hardly allow drawing quantitative conclusions on the real benefit of the presence of horizontal reinforcement to the performance improvement for a specific masonry type. The experimental campaign presented in this paper includes a set of in-plane cyclic tests on Autoclaved Aerated Concrete (AAC) masonry panels with thin horizontal and vertical joints filled with thin layer mortar, made both in unreinforced and bed-joint reinforced masonry with flat-truss bed-joint reinforcement. The direct comparison of the results, along with specific tests performed on wallettes made with the two different construction technologies, allows the assessment of the effectiveness of the horizontal reinforcement in enhancing the in-plane seismic performance of AAC masonry.

Prestress loss due to creep and shrinkage of high-strength calcium silicate element masonry with thin-layer mortar

Data on creep and shrinkage of high-strength calcium silicate element masonry with thin-layer mortar (CASIEL-TLM masonry) is not currently available in international literature. A novel application of this material in unbonded post-tensioned shear walls requires creep and shrinkage data to predict prestress loss. Therefore, creep and shrinkage were measured on 38 large-scale high-strength CASIEL-TLM specimens, including a TLM bed joint or a wall-floor connection, for a period of 300 days. Initial moisture content of the specimens and temperature and relative humidity of the environment were carefully controlled. Creep and shrinkage data were used to predict prestress loss by means of visco-elastic finite element simulations as well as a simple analytical expression. These predictions were validated by prestress loss experiments, conducted simultaneously with the creep and shrinkage experiments. Predictions for final prestress loss due to creep and shrinkage are below 16 or 24 % for CASIEL-TLM masonry with prestressing strands or prestressing bars respectively.

UPT rectangular and flanged shear walls of high-strength CASIEL-TLM masonry: Experimental and numerical push-over analysis

The mechanical behaviour of unbonded post-tensioned (UPT) shear walls of high-strength CAlcium SIlicate ELement masonry with Thin-Layer Mortar (CASIEL-TLM masonry) was investigated experimentally and numerically. Eight walls were tested with the following key variables: unit type, prestress level and cross-sectional shape (rectangular or T-shaped with interlocking of web and flange). An extensive measurement scheme was adopted that allowed derivation of average curvatures and strains in the bottom region of the wall in addition to wall displacements. Since UPT masonry is characterised by the absence of local compatibility between masonry and the UPT tendons, a numerical model for quasi-static, monotonic push-over analysis was developed that provides an iterative solution for the global interaction between masonry and UPT tendons. A common masonry stress–strain diagram was adopted in the numerical model. A peculiarity of CASIEL-TLM masonry is the kicker course, which reduces the stiffness of the bottom region of the shear wall. This layer was modelled with no-tension, linear-elastic behaviour and a reduced stiffness. Nevertheless, the model underestimates the experimental deformations of the rectangular shear walls, while the strength is in reasonable agreement. The walls with T-shaped cross-section failed prematurely by shear of the web-flange interface, resulting in diagonal splitting cracks in the interlocking units. This paper deals with the experimental results of UPT CASIEL-TLM masonry shear walls with rectangular and T-shaped cross-section and with the numerical modelling of the overturning behaviour of UPT shear walls with rectangular cross-section.

Flexural strength of low density blockwork

The characteristic flexural strength of low density aircrete wallettes (2.8 and 2N/mm2) incorporating both conventional and thin layer mortar is verified. The wallettes are tested in accordance with British and European standards. The flexural strength of aircrete wallettes is derived from the strength of small specimens tested to destruction under four-point loading. The strengths of the wallettes are high with impressive repeatability with the maximum strength being reached for thin layer wallettes within 7days curing time. In general the strengths of both conventional mortar and thin layer mortar wallettes compare favourably to values reported in the standards.

A simplified mechanical model to assess the bearing capacity of masonry walls: Theory and experimental validation

This paper deals with the bearing capacity of masonry walls under lateral loads. Four different series of experimental measures have been collected, representing a total number of 20 walls tested at the Scientific and Technical Center for Buildings (CSTB, France). The constitutive materials of the walls and the geometrical features of the walls are: – Orthotropic blocks (masonry or concrete units), with either horizontal or vertical cells. Their geometrical dimensions are such that the thickness is either equal to 0.2 m or 0.38 m while the ratios (height/length) range from 0.4 up to 1. The compressive strength of the blocks are in relative ratios (horizontal/vertical strengths) ranging from 0.11 up to 3.11. – Joints made of mortar or thin layer mortar. The vertical joints might be either empty or full while the horizontal joints are full for the whole experiments reported herein. – Walls with lengths ranging from 1 m up to 3.75 m while the height range from 2.5 m up to 2.8 m. An existing model, relying on the principle of wall failure by its diagonal in compression, has herein been applied and its results have been compared with the experimental values for the 20 available walls. The model for compressive diagonal provides results that range within the interval (0.52 up to 2.67) times the experimental bearing capacity of the masonry walls. The authors have therefore developed a simplified model that assumes that the wall fail by induced tension in the perpendicular direction of the diagonal of either the blocks or the walls. Compared to the experimental values collected in this paper, this simplified mechanical model provides theoretical bearing capacity values that are in good accordance with the observed values.

Micro-chemical/structural characterisation of thin layer masonry: A correlation with engineering performance

Masonry is one of the most ancient methods of construction. The types of blocks and mortars used over the centuries have developed considerably with the introduction of various types of materials. A multidisciplinary investigative approach, involving both engineering and material sciences expertise, will be necessary for a complete evaluation of the behaviour of masonry elements. From the engineering point of view, the transverse lateral load capacity of masonry built using solid dense concrete blocks with thin layer mortar, is up to four times that of similar blockwork constructed using conventional mortar. Both the mortar and block constituent material’s properties alter the joint strength with enhancements to tensile flexural bond strength. When thin layer masonry technology (TLMT) is employed, in conjunction with solid dense concrete blocks, the masonry behaves more as a concrete plate than conventional blockwork. The engineering properties of masonry elements are not only related to the engineering properties of the blocks and mortars used, but also to how the bond at their interface interacts. Testing on two different block types, and one mortar was undertaken to verify this hypothesis. Engineering testing was carried out to determine the flexural strength of the material. This approach was combined with petrographical examination of the two different types of block and the bond zone using micro-analytical techniques, (OTLM, SEM and EMPA). Observations using SEM and EMPA techniques revealed that these differences depend on the composition of both blocks and mortar, and in particular they are related to the petrographical composition of the parent material of the block. These aspects affect how the bond layer forms and influence the mechanical properties of the joint.