CHAPTER II
LITERATURE REVIEW
2.1
Introduction
The history of interlocking bricks began in the early 1900s with the construction of toys for children’s McKusick (1997), Love and Gamble (1985). Amongst the first inventors of the toy systems that contributed to the mortarless technology (arrangement of parts that construct ideal structures) were: 1) The Englishman Frank Hornby (1863 – 1936) of Liverpool, with Meccano sets, 2) A.C Gilbert (1884 – 1962) of Salem, Oregon with Erector sets, 3) Charles Pajeau who invented Tinker Toy construction sets in 1913. He was a stonemason from Evanston, Illinois, USA, 4) John Lloyd Wright who invented Lincoln Logs in 1920, and 5) Ole Kirk Christiansen (1891 – 1958), who invented Lego.
2.2
Characteristics of lateritic soil bricks fired at low temperatures
Mbumbia et al. (2000) have conducted a research work on the advance of physical and mechanical properties of some Cameroonian lateritic soil bricks which were stabilized through heat at very low temperatures, with a sight to finding their appropriateness for the construction of walls of simple houses. The main advantages are economy and the encounter of ‘cultural choice and practice’ of people of the region of study. In this study no admixture (which was made by lime, cement, bentonite, etc.) is used. By crushing raw materials, the effect of the homogenization will be achieved. The cohesion of clay present in raw materials and the cementitious binder, which is caused by the transformation of some mineral phases at low temperatures, have been exploited. In order to solve this case a detailed experimental programme was carried out to find density, volume change, water absorption, modulus of rupture (flexure test), compressive strength and erosion by the test specimens consisted of 105×30×25
5
mm3 units which were made by lateritic soil was collected from Etoug-Ebe, an area of Yaounde town with a particle size percentage of 2% gravel, 28% sand, 31% silt, and 39% clay. They have conducted that water absorption decreased with temperature until 550
where it began to increase and achieved a local maximum (approx. 28.2%)
at approximately 750 . From this temperature, the water absorption decreased with temperature. Also compressive strength increased with temperature which is varied from 2.9 MPa at room temperature (27
) to 3.09 MPa so the average compressive
strength at room temperature is 2.90 MPa, and modulus of rupture is changed from 0.96 MPa to 1.06 MPa so the average flexural strength is 1.00.
2.3
Enhancing Bond Strength and Soil-Cement Block Masonry
Reddy et al. (2007) have conducted a research on the soil-cement blocks which were utilized for the load bearing masonry of 2–3-story buildings. Flexural and shear strength of walls made by these blocks depend upon the bond strength between the block and the mortar. Mostly 6–10% cement is used for soil-cement blocks making which is based on the strength requirement. Consequently, the reconstituted soil mixed with 8% Portland cement (by weight) was used for the manufacture of soilcement blocks by 305 143 100 mm size using a fixed stroke length manually operated machine. Soil-cement blocks were shown in Figure 2.1.
FIGURE 2.1 Soil-cement blocks (left to right: plain surface, rough textured bed face, and frogs on the bed face)
Methods of ameliorating the shear-bond strength of soil-cement block masonry without changing the mortar characteristics and the influence of shear-bond strength
6
on masonry compressive strength were discussed in this paper. Modifying the texture of bed faces of the block, size and area of the frog, and certain surface coatings have been tried to improve the shear-bond strength. Parameters which were discussed in this research are: 1) procedure for obtaining different surface texture and frogs on the Soil-Cement Block Surface, and 2) experimental program and experimental methods such as compressive strength and flexural strength of blocks, stress-strain measurements for soil-cement blocks and mortars, masonry triplet tests, and compressive strength of masonry and stress-strain relationships. The results of compressive strength, flexural tensile strength, water absorption, and initial rate of absorption for soil-cement blocks are given in Table 2.1 which gives mean values, ranges of values, and the number of specimens tested.
TABLE 2.1 Strength and Absorption Characteristics of Soil-Cement Blocks Properties of the block Wet compressive strength (MPa)
Wet flexural tensile strength (MPa)
Initial rate of absorption (%)
Saturated water content (%)
Mean values Number of specimens 8.34 (7.86–8.87) 1.21 (1.18–1.24) 3.21 (2.47–3.91) 12.02 (11.6–12.7)
10
6
15
6
Note: Dry density of the block: 18 kN/ m; rang values are in parentheses
Dry density of the soil-cement blocks is kept constant at 18 kN/ m3. Wet compressive strength of the soil-cement block is 8.34 MPa, while the flexural strength is 1.21 MPa (i.e., about 15% of compressive strength). Saturated water content of the block is 12.02% and initial rate of absorption is 3.21 kg/m2/min. usually soil-cement blocks have higher initial rate of absorption when compared to burnt clay bricks (Walker 1999; Reddy and Gupta 2005a).
7
2.4
Compressed-stabilized earth brick
Muntohar (2011) has performed a research work on utilization of lime and rice husk ash for soil stabilization caused high strength increase and other geotechnical properties of the stabilized soils. Its application lime and rice husk is better for construction materials than compressed-stabilized earth (CSE) or unfired-brick. Studying on materials, lime and rice husk ash (RHA), mixture proportion and sample mixture, compressive strength of the stabilized earth brick, water absorption of the stabilized earth brick, and flexural strength characteristic of the stabilized-earth beam are factors which have been considered in this paper. Mixtures proportion, which was shown in Table 2.2, and sample preparation will be obtained by clay as the basic material of brick mixed with sand in order to reduce the effect of shrinkage. A trialmix of soil and sand were carried out to find optimum value of sand used based on their compaction characteristics. The variation of clay and sand mixtures were assessed by standard Proctor compaction test. The optimum proportion of soil–sand mixtures is about 70% soil and 30% sand which has highest the maximum dry density among the trial-mix. The optimum moisture content and maximum dry density the soil–sand mixture are 19% and 17.4 kN/m3 respectively. For a comparison, a clay soil specimen was also investigated. Muntohar has conducted that: 1) the possibility of blended binders use with clay for the manufacture of unfired clay materials in the building industry and different stabilized soil applications, 2) The strength characteristics of the unfired clay bricks were meliorated by lime and RHA which their combined action strongly bound the soil particles, 3)Adding sand to the mixing materials in stabilized clay resulted in more improvement in the water retention ability of brick, 4) Performances of clay brick in compressive and flexural strength improved by mixing the mixture with sand, and they become better by adding lime and RHA as demonstrated in Figure 2.2 and Table 2.3 and the optimum quantity of lime and RHA to achieve highest strength is obtained at the ratio 1:1, 5) the addition of lime and RHA mixture ratio reduced the ability of the compressed stabilized earth to absorb water, and 6) the compressive strength because of submersion in water mostly remains 62–95% of the normal (dry) compressive strength specimen.
8
TABL 2.2 Mixture design of samples to do compressive strength and water absorption test Proportion of raw materials Clay
Specimen number
Sand Lime: Rice hask
100%
_
_
1
90%
_
5%:5%
2
5%:10%
3
5%:15%
4
10%:5%
5
15%:5%
6
_
7
5%:5%
8
5%:10%
9
5%:15%
10
10%:5%
11
15%:5%
12
70%
30%
9
FIGURE 2.2 Effect of lime and RHA ratio on the compressive strength (a) clay specimen,(b) clay–sand mix specimen
10
TABLE 2.3 Compressive strength (MPa) Lime: RHA ratio
2.5
Dry
Wet
Clay Clay-Sand Clay Clay-Sand
0
13.3
11.2
–
–
1:3
16.7
14.9
10.4
12.0
1:2
18.1
17.7
11.8
15.1
1:1
20.7
18.6
15.5
16.1
2:1
17.3
16.6
14.8
15.2
3:1
15.4
13.0
13.8
12.4
Harakeke reinforcement of soil–cement building materials
Segetin et al. (2007) have conducted a research on fibre from the New Zealand flax plant, Phormium tenax, or Harakeke as it is otherwise known in Maori, has been used to reinforce soil–cement composites in an effort to make better the strength and ductility of the composite material, in other words to improve the mechanical properties of the soil–cement composite. Prior investigations have found the interfacial bond strength between the harakeke fibre and the soil–cement matrix to be a significant issue for composite strength and in order to improve it; an enamel paint coating has been applied to the fibre surface. Aims of this research implementation are focuses on the development of soil–cement building materials suitable for the construction of habitable dwellings in New Zealand. In order to carry out this project they have considered different factors in subdivision parts such as: 1) soil stabilization and reinforcement based on chemical stabilisation and fibre-reinforcement, 2) materials, 3) fibre mixing manually and mechanically by cultivator or rotary-hoe, concrete mixer, and tumble mixer, 4) specimen preparation, 5) flexural testing, 6) and compressive testing. The soil was sourced from a local quarry which was classified as very silty SAND comprising 20% silt and 77% sand particles and due to stabilize it Ordinary Portland cement was employed. In order to coating the flax fibres enamel paint diluted by mineral turpentine. According to compressive strength and flexural test they have conducted that: 1) maximum flexural strength of no fibre-reinforcement specimen was 0.427 MPa and the average value was 0.26 MPa while the flexural
11
strength of fibre- reinforcement specimens was in the range of 0.35-0.5 MPa, and 2) Specimens without fibre-reinforcement have an average compressive strength of 1.79 MPa with a standard deviation of 0.5 MPa, while the coated and non-coated fibrereinforced specimens which were shown in Figure 2.3 have compressive strengths of 2.0 and 2.49 MPa, respectively, with standard deviations of 0.43 and 0.5 MPa. Average compressive strength taken over all of trialled specimens was 2.14 MPa which exceed the minimum requirement of 1.3 MPa indicating that in terms of compressive strength the material may be suitable for building construction. The compressive strength for both coated and non-coated fibre-reinforced specimens are greater than for the non-reinforced specimens. The dramatic improvements in the compressive strength of the soil–cement composite provided by Duracem cement which has the average compressive strength from 2.14 to 4.55 MPa.
FIGURE 2.3 (a) coated fibre-reinforced specimens and (b) non-coated fibre-reinforced specimens
2.6
Experimental testing and finite-element modelling for clay masonry
Porto et al. (2010) have done researching on defining the in-plane cyclic behaviour of three types of load-bearing masonry walls made by perforated clay units, and various types of head and bed joints were performed. Experimental behaviour was modelled with four types of nonlinear finite-element models. Isotropic or orthotropic material laws were chose for macromodeling and micromodeling schemes. Two easy criterions were recommended for calibrating the models, one for defining orthotropic properties
12
starting from perforated unit geometry and the other for defining expanded unit and interface element properties in micromodels. The procedures accepted for model calibration established the reliability of various modelling strategies. Masonry made with pockets for mortar infills (Po) have fully filled head joints as mortar is provided over a minimum of 40% of the unit width. Masonry made with tongue-and-groove units (TG) was built with dry mechanical interlocking between units at the head joints. Thin-layer joint masonry (TM) was built using thin layer mortar at the bed joints and dry mechanical interlocking between the units at the head joints. All these three types were shown in Figure 2.4.
(a)
(b)
(c)
FIGURE 2.4 Three types of clay units: (a) edge-ground unit (TM); (b) unit with tongue and groove (TG); and (c) unit with mortar pocket (Po)
Cross section design (250 300 mm; shell and web arrangement), percentage of holes (43%), and mean compressive strength (20 N/ mm2) were almost the same in all units. Thin-layer mortar (TM; bed joints of 1.3 mm thick) and general-purpose mortar used for specimens with ordinary bed joints (TG and Po; bed joints of 12 mm thick). Parameters considered in this research are tests on small masonry assemblages, uniaxial and diagonal compression tests, in-plane cyclic shear-compression tests, calibration of continuum models, calibration of interface models, and validation of models and results of analyses. According to the uniaxial and diagonal compression tests, which is done on specimens with average dimension of 1000 1000 300 mm,
13
they have conducted that mean compressive strength of TM is 6.95 N/mm2 and for TG equals to 5.67 N/mm2 while for Po is 5.34 N/mm2. TM masonry compressive strength with thin-layer joints was 23% higher than in TG with ordinary bed joint and interlocking units, and TM specimens have lower de-formability to vertical loads than TG specimens, also the compressive strength and elastic moduli of TG and Po (mortar pockets) masonry were practically equal, although the latter had lower values of compressive strength ( 6%). The experimental perforated clay units were designed on purpose for this research, following the principles of “robustness.” They had compressive strength of about 20 N/ mm2, whereas the compressive strength of perforated clay units used in practice varies over a range of about 20–5 N/ mm2. Therefore, in order to study the influence of unit compressive strength (fcu) on the global shear behaviour of the three masonry types, analyses were repeated with units with compressive strengths of 20, 15, 10, and5 N/ mm2.
2.7
Load bearing soil-cement brick walls adding ground ceramic waste
Jr. et al. (2003) have conducted an experimental study of three load bearing walls made by soil-cement bricks manufactured by three different material proportions, in which two of them had part of the cement amount replaced by crushed ceramic waste. Proportion of materials mentioned before are as follows: mixture 1 – 15.8% of soil moisture, 6% of binding material and without any replacement of Portland cement by crushed ceramic material; mixture 2 – 15.8% of soil moisture, 6% of binding material and 35% of replacement of Portland cement by crushed ceramic material; and mixture 3 – 15.8% of soil moisture, 8% of binding material and 55% of replacement of Portland cement by crushed ceramic material. Compressive strength of soil-cement brick and cylindrical specimen and walls made by these soil-cement bricks are the major factors mentioned in this paper. Soil-cement brick dimension and brick specimen size for compressive strength were shown in Figure 2.5 and 2.6 respectively.
14
FIGURE 2.5 Soil-cement brick dimension
FIGURE 2.6 Compressive brick specimen
The walls were 95.20 cm height, 75.32 cm width, and 12.56 cm thickness and had their bricks layered with cement paste. The walls were tested under compression and their displacements were measured with 5 dial gages. They have conducted that: 1) the cylindrical compressive strength of the mixtures 1, 2, and 3 were 5.62, 3.84 and 3.14 MPa, respectively, along with the average specific masses were 2024, 2001 and 1980 kg.m-3 respectively, 2) the compressive strength of bricks made by mixtures 1, 2, and 3 are 3.07, 2.11, 2.19 MPa respectively with the average specific mass of 1648, 1689 and 1760 kg.m-3 correspondingly, and 3) the compressive stress, in wall 1, at the failure was 2.46 MPa, which is 20% less than the brick strength whilst in wall 2 was 2.21 MPa, that is almost the same brick strength and in wall 3 was 2.05 MPa, which is close to the brick strength. Finally, it was observed that bricks with 55% of cement
15
replacement by crushed ceramic waste are suitable to be used as structural elements in popular housing.
2.8
Interlocking soil-cement bricks wall
Ahmad Z. et al. (2011) investigate the behaviour of masonry walls by soil-cement interlocking bricks. The materials for manufacturing the interlocking brick consists of cement, laterite soil and sand with ratio of 1:1:6 (cement: sand: soil) by volume. The corresponding mixing mass ratio of the reference sample is 27.6:4.0:4.2 kg. Soil, sand, and cement were mixed together in the drum mixer. Water was gradually added into the mixer until having right consistency which ready for moulding. The mixture was placed into a mould as shown in Figure 2.7a and manually pressed under certain amount of pressure (about 1.0 MN/m2) to become solid and rigid with the interlocking shape. Then the specimen was removed from the mould and leave to air cured for 24 hours. The natural drying is used for drying process where the bricks are stacked on racks and dried by the circulation of unheated air as shown in Figure 2.7b.
FIGURE 2.7 Interlocking brick; (a) mould for pressing and (b) curing process
The bricks sizes are 250 mm length, 125 mm width and 100 mm height. Purposes of doing this research work are determination of: 1) physical properties of the brick unit such as density, dimension, and water absorption, and 2) compression
16
and bending of brick unit and wall. In order to reach aims of the project they have done sieve analysis, hydrometer test, and compressive strength test of brick units and masonry walls which were constructed from interlocking bricks and tested under constant vertical load at different eccentricities. Physical and mechanical properties of the interlocking brick unit were shown in Table 2.4.
TABLE 2.4 Physical and mechanical properties of the interlocking brick unit
Length(mm) Width(mm) Height(mm)
Compressive strength(N/mm2) Mean
249.2
125
Water absorption (%)
COV (%)
98.8
18.8 7.5
13
According to BS3921:1985, they have conducted that the average of compressive strength of single unit interlocking soil bricks is 7.5 N/mm2 which is decreased to 3.56 N/mm2, the amount of compressive strength of the wall. In the masonry interlocking brick walls, the eccentricity of the loading influenced the value of strength of the wall. The strength is reduced when the eccentricity is away from the centre.
2.9
Flexural strength of compressed stabilized earth masonry materials
Jayasinghe and Mallawaarachchi (2009) have conducted a research work on the flexural strength of masonry. Flexural strength, which is defined parallel and perpendicular to bed joints, is a vital strength factor particularly in lightly loaded walls. The aim of the implementation this project was searching on compressed stabilised earth (CSE) wall in order to determine the flexural strength using panels subjected to limited degree of pre-compression and appraise the effects of different bond patterns possible with CSE bricks on the flexural strength characteristics to attain enhanced performance when subjected to lateral loads using cost effective means. Alternative masonry materials are promoted because of scarceness of conventional masonry materials and energy related issues associated with them. In
17
order to solve this case a detailed experimental programme was accomplished to find the flexural strength of an assortment of options possible with CSE masonry that is made by laterite soil, which has special feature of possibility to stabilise with relatively low percentage of cement, and comparing the flexural properties of CSE masonry with that of conventional masonry. A cost effective method for intensification the lateral resistance was proposed. In order to perform this project they study compressed stabilized earth in subdivision of solid bricks, plain solid blocks, interlocking solid blocks with a horizontal groove, interlocking hollow blocks, and rammed earth which are all shown in Figure 2.8-2.11.
FIGURE 2.8 CSE brick
18
FIGURE 2.9 CSE plain solid blocks
FIGURE 2.10 CSE interlocking solid block
19
FIGURE 2.11 CSE interlocking hollow block
CSE masonry is one such material with sufficient compressive strength for single and two storey load bearing construction. Flexural strength of such alternative materials is significant to appraise the performance when subjected to lateral loads due to wind, floods or any other load that can cause out-of-plane bending in a wall. The stabilization factor used to create compressed stabilized earth was cement. The flexural strength of different walling brick shapes were demonstrated in Table 2.5.
20
TABLE 2.5 Flexural strength of different walling based on brick dimension Dimensions of an individual unites(mm)
Type of walling materials
Flexural strength(N/mm2)
Parallel to
Perpendicular to
bed joints
bed joints
75
0.3
0.9
225
115
0.243
1.284
235
225
115
0.393
1.957
300
145
100
0.262
0.261
Length
Width
Height
225
115
225
Burnt clay bricks of water absorption >12% [13] CSE solid brick CSE interlocking solid brick CSE interlocking hollow brick
The results were compared with the values achieved for conventional masonry to highlight the appropriateness of compressed stabilized earth masonry for wider application with confidence. They have conducted that lateral load carrying capacity of a wall which was lightly loaded in compression is controlled by flexural strength. An experimental programme indicates that the flexural strength of CSE wall panels subjected to low levels of pre-compression are about 0.25 N/mm2 or above by comparing these values to BS 5628: Part 1:1992 for walls constructed with burnt clay bricks which have water absorption above 12%. With compressive strength results, it can be said that CSE bricks, blocks, and rammed earth can be considered confidently as viable and safe options for the single leaf external and internal load bearing walls of single and two storey houses. Single leaf walls are usually used for houses in countries with tropical climatic conditions.
21
2.10
Water permeability assessment of alternative masonry systems
Anand et al. (2003) have conducted a research work on water penetration resistance of conventional brick/block masonry for different construction types and materials approving ASTM E 514-90 procedure which demonstrates most generally approved method for laboratory investigations for evaluating the effect of different materials, coatings, construction details, and workmanship on water penetration resistance of masonry subjected to wind-driven rain. The behaviour of the interlocking block masonry based on the bedding type (dry-stacking, thin-jointing, and mortar-bedding), surface finishes (stucco/plaster finish) have been looked into. In order to solve this case they have done the relative performance of solid and hollow interlocking block masonry system, developed by the authors, with : 1) conventional masonry by testing on burnt clay solid brick masonry in order to know the influences of joint thickness, two types of brick and surface finish; also for relative performance appraisal with interlocking block masonry, 230 mm thick single with the brick masonry wall in English bond and 200 mm thick concrete hollow block masonry in running bond with structurally efficient blocks used which is shown in Figure 2.11, and 2) testing on solid and hollow interlocking block masonry, which are shown in Figure 2.12 and Figure 2.13; these blocks which were developed by authors are assembled to have walls with half-course (100 mm) high units on one face and full course (200 mm) high units on the other face placed on a layer of levelling course of mortar. Following layers of full-course high units are stacked on inner and outer faces and finally end up with half-course units as closures. Specimen thickness was 150 mm for SILBLOCK masonry and 200 mm for HILBLOCK masonry.
FIGURE 2.11 Structurally efficient hollow blocks (dimensions in mm)
22
FIGURE 2.12 SILBLOCK (dimensions in mm)
FIGURE 2.13 HILBLOCK (dimensions in mm)
They have conducted that the mean compressive strength of the wire-cut burnt clay brick based on 10-20 mm joint thickness is 12 MPa with water absorption of 8% while table-moulded brick have 6.4 MPa mean compressive strength value with the water absorption equals to 11.9% and masonry with both types of units (with a mortar joint thickness of 10 mm) was finished with 1:5 cement–sand plastering have compressive strength of 7.2 MPa and flow value of 112% on the test face. Also the comparison of the SILBLOCK masonry with brick masonry was illustrated in Table 2.6.
23
TABLE 2.6 Properties of masonry unites Unit type SILBLOCK
24-hr water absorption(% by weight) Compressive strength(MPa) 6.2
7.1
11.9
6.4
5.9
10.7
Table-moulded burnt clay brick HILBLOCK
2.11
Fatigue behaviour of grouted stabilised of interlocking brick masonry
Nazar and Sinha (2007) have conducted a research work on the fatigue behaviour of interlocking grouted stabilized mud-fly ash brick masonry. In order to carry out this project the brick units and masonry system developed by Sinha is used. In order to reach the aim of research brick masonry specimens have been constructed from interlocking stabilized mud-fly ash bricks of size 200 mm
100 mm
100 mm
indicated in Figure 2.14 and compressive strength and the standard deviation of them illustrated in Table 2.7, also eighteen specimens of size 500 mm × 700 mm × 100 mm and nine specimens of size 500 mm × 500 mm × 100 mm were tested.
FIGURE 2.14 Interlocking brick
24
TABLE 2.7 Properties of interlocking bricks and grout
Type of material
Mean
Standard
compressive
deviation
strength (MPa)
(MPa)
0.50
12.12
1.41
0.40
38.30
4.25
Mix proportion by
Water/cement
weight
ratio (%)
Interlocking
0.60 Natural soil:
stabilized
0.25 fly ash: 0.15
mud-fly ash
cement
brick Cement + non-shrink Grout
material @225 gm per 50 kg of cement
Three cases of loading at 0°, 45°, and 90° to the bed joints were considered. For each of three levels of minimum stress, the number of cycles to failure is determined for each of various maximum stress levels considered. These tests are limited to around 8000 load cycles. According to the test results average ultimate strength for specimens loaded at 0 , 45 and 90 to bed joints were 6.49, 5.23 and 7.45 N/mm2 with a standard deviation of 0.37, 0.29 and 0.24 N/mm2, respectively. And the average axial strain corresponding to peak stress, for specimen loaded at 0 ,45 and 90 to bed joints were3.56 10-3, 1.83 10-3 and 3.32 of 1.56
10-4, 1.36
10-4 and 1.48
10-3 with a standard deviation
10-4, respectively. They have conducted
behaviour of interlocking grouted stabilized mud-fly ash brick masonry under fatigue loading. The compressive strength of interlocking grouted brick masonry decreased up to 25% under frequent compressive loading and at the high value of i, the increase of axial strain with the number of load cycles remained approximately linear. Initially at lower values of
i,
the increase of axial strain with the number of cycles was high,
after that a relatively lesser rate of increase of strain with the number of load cycles and finally a rapid increase of strain near failure. Also the relation between
i
and log
Nf recommended a linear variation for each level of σmin, for the range of
i
considered. For a given value of i, the number of load cycles to failure considerably increases when the value of σ min increases. A linear relationship exists between σ max
25
and log Nf. Also the number of cycles to failure increases as the value of σ max was decreases for each three levels of σ min considered. The plastic strain in the material with σmin equal to 0.25 and 0.50 were notably higher than the plastic strain values when unloading was finished to zero stress level. This phenomenon stated by the shape of a typical unloading curve which in the beginning demonstrates higher stiffness at the beginning of unloading and the slope of the unloading curve bit by bit decreases as unloading is continued. The unloading curve then noticeably softness at low stress levels as if it is being pulled inward and then terminate at zero stress level.
2.12
Water permeation of interlocking block masonry
Anand and Ramamurthy (2001) have conducted a research work to water penetration resistance of a solid interlocking block masonry system, based on ASTM E 514-90 for the effect of the bedding type (dry stacking, thin jointing, and mortar), surface finishes (stucco and plaster on one side or both sides), and modelled wind velocities (0, 50, and 100 km/h). By considering three parameters such as :1) type of bedding according to three method of dry stacking of the blocks with pointing of joints; thin jointing (2–3 mm thick) with mortar slurry (1:3 cement: fine sand) of flowing consistency; and mortar bedding (10 mm thick) as per ASTM C 270 (ASTM 1989); 2) type of surface finish for all type of bedding are looked at no surface finish; surface finish on test face alone; and finish on both faces; and 3) Simulated wind velocity- as high winds generally take place just for a small percentage of a rain duration, besides the ASTM E 514 recommended pressure of 500 Pa (corresponding to a wind velocity of 100 km/h), tests were also completed with 0 pressure and 120 Pa (equivalent to 50-km/h wind velocity). The influence of wind velocity (represented as equivalent pressure) is reported for masonry with a surface finish on the test face. Dampness and leakage appear early with an increase in pressure for both stucco and plaster finishes. The total leakage and dampness become more with these two variables, but the degree of influence changes with construction and finish type. Anand and Ramamurthy have concluded that: (a) Silblock masonry without a surface finish is appropriate for rainprotected and interior walls, (b) External face protection, by either stucco or plaster, decreases the leakage and dampness. A plastered finish was more effective than the 3mm-thick stucco finish,(c) The introduction of any form of the mortar bedding (thin
26
jointing or conventional) effected higher dampness than dry-stacked specimens,(d) For severe exposures when pressure is 500 Pa, plastering is effective in reducing dampness and total leakage through all three types of bedding whereas the stucco finish is only effective with the dry-stacked specimen, (e) Judging the overall behaviour of plastered specimens with respect to (1) dampness, dry-stacked masonry executes better; and (2) leakage, thin-jointed masonry does better.
2.13
Strength correlation between load bearing interlocking mortarless hollow
block masonry Jaafar et.al (2006) have done research on the development of the compressive strength correlation between the individual block, prism and basic wall panel for load bearing interlocking hollow mortarless blocks which were developed by the Housing Research Centre at Universiti Putra Malaysia. The Compressive strength, interlocking mechanism, crack patterns, and failure mechanism of the interlocking masonry specimens are highlighted and discussed. Forty individual block units from stretcher, corner, and half blocks, which were shown in Figure 2.15, tested under compression. Dimensions of these interlocking blocks were indicated in Table 2.8.
(a)
(b)
(c)
FIGURE 2.15 Interlocking block unite; (a) stretcher block, (b) corner block, and (c) half block
27
TABLE 2.8 Interlocking block dimension Block type Length(mm) Width(mm) Height(mm) Stretcher
300
150
200
Half
150
150
200
Corner
300
150
200
The compressive strengths of 10 prisms assembled by stacking two stretcher blocks and two half blocks were evaluated. Furthermore, four wall panels each having a dimension of 1.2 m × 1.2 m were assembled and tested under axial compressive loads. The results were compared with those found in bonded masonry. Compressive capacity of the bonded masonry predicted by BS 5628 Part 1:1992. The correlations between the compressive strength of the interlocking masonry individual block (f cb), prism (fcp) and standard panel (fcw) found in this analysis were fcp= 0.47 fcb, fcw= 0.83fcp and fcw= 0.39fcb. Test results indicate that failures were due to the development of cracks which occurred at the interface between the web and shell; the cracks widened with increase in the applied load until failure and vertical cracks in the block shells developed with increase in the applied load, also the cracks in the shells were vertical and aligned with the vertical joints. Moreover results of tests illustrate that interlocking mechanism and strength of the block in the load-bearing wall was satisfactory.
