Mortar-Chap 6 @CE506 PPT (1).pptx semester 3

Cem note 1 sem 3

1. Chap 6. Mortar (2 Hrs, Marks 3/40)  6.1 Introduction 6.2 Classification of Mortar. 6.3 Function of mortar 6.4 Selection of Mortar for Civil engineering works. 6.5 Tests for mortars:

2.  6.1 Introduction: Building mortar is defined as a mixture of binding materials like cement or lime, fine aggregate like sand or surkhi and water acquiring stone like properties with considerable strength as a result of hardening. The safety, strength and durability of the any structure therefore depend on the quality of the mortar used.   Mortars are used for filling joints as a binding material in stone or brick masonry, for preparation of decorative and protective material to walls in the form of plasters. The ingredients of mortars used for various engineering works are: Binding materials such as cement, lime etc Fine aggregates such as sand, surkhi, cinder etc. and Water Mortars are usually named according to the binding material used in their preparation such as cement- mortar, lime- mortar, lime-cement mortars or gauged mortars, mud mortars, etc.

3. Special mortars: Mud mortars Cement- clay mortars Decorative mortars Fire resistant mortar Air-entrained (plasticized ) mortar. Sound absorbing mortar(600-1200 kg/m3) Packing mortar Chemical resistant mortar X-ray shielding mortar Light weight mortar <1500 kg/m3)

4. Classification Based on Binding M aterial: Lime mortar: Non – hydraulic lime mortars: The fat lime shrinks to a great extent and therefore it requires 2 to 3 times i.e. 1:2 or 1:3 by volume of sand . The lime should be well slaked before use. Properties: This mortar is suitable only for thin joints in brick work and stone work This mortar is unsuitable for water logged areas or in damp situations. It sets slowly in presence of air. This mortar hardens very slowly. It does not cause efflorescence. This mortar possesses high degree of plasticity. Hydraulic lime mortars: The mixing proportion of lime to sand is about 1:2 by volume. This mortar possesses more strength and can be used in water logged or in damp situations . It is sufficiently durable, hardens slowly and shrinks very little. This type of mortars is generally used for lightly loaded above ground parts of building. The mortar once prepared should be consumed within 60 minutes of mixing of water.

5. Black mortars: As name signifies, the color of this mortar is black. The usual proportion is 1 part lime to 3 parts of ash or cinder . Due to its awkward color, these are used in less important temporary work and in internal walls.   Lime- cement mortar or gauged mortar or composite mortar: In order to improve the quality of lime mortar and to achieve early strength, the Portland cement is sometimes added to it. This process is known as gauging. The usual proportion of cement to lime by volume is about 1: 6 to 1:8 . Such mortars are more economical, stronger, durable and denser than ordinary lime mortars. This mortar may be used for bedding and for thick brick walls. It is also used for plastering wall surfaces and outside weather proof pointing. Surkhi mortar: This type of mortar is prepared by surkhi (powder of burnt brick) and lime (1:1) or lime, surkhi and sand (1: ½: ½). This ratio of lime to surkhi will depend on the nature of job where the mortar is to be used. The surkhi mortars are use for ordinary masonry work of all kinds in foundation and superstructure. But it cannot be used for plastering or pointing since surkhi is likely to disintegrate after some time.   Gypsum mortar: This type of mortar is rarely used in tough construction . These are prepared from gypsum binding materials such as building gypsum and anhydrite binding materials.

6. Cement mortar: In this type of mortar, cement is used as binding material. The ratio of cement and sand may vary from 1:2 to 1:8. This mix proportions depends on types of work, requirements of strength of mortar etc. This mortar should be consumed within 30 minutes after mixing as they set and harden very quickly. The cement mortar is used where a mortar of high strength, grater durability and greater water resisting properties is required such as in underground constructions, water saturated soils etc. It is observed that 1:8 cement mortars is nearly twice as strong as 1:3 lime mortar . Cement mortar is the best form of mortar for plastering and pointing of walls. Cement mortar when used for protective plaster provides a water proof layer and protects the elements covered from weathering effects such as alternate heat and cold, frost action, freezing and thawing action, rain, wind, atmospheric impurities etc.     Preparation of cement mortar: The following are the two basic methods of cement mortar preparation. Hand mixing method, and Machine mixing method:  

7. Hand mixing method: This method is adopted for small scale unimportant works and involves following main steps : Spreading of sand in a uniform layer on impervious platform. Spreading of appropriate quantity of cement on top of the sand layer. Mixing of sand and cement thoroughly with shovel, turn the mixture over and over until the whole dry mass becomes uniform in color. Creating of volcano shaped depression on the middle of platform, and pour required quantity of water. Mixing of sand and cement mass thoroughly with shovel, turn the mixture over and over until the whole mass becomes uniform in color. Mixing should be continued till a mortar of uniform consistency is obtained. Water in small quantity at a time can be added to achieve uniform and homogeneous mix. Cement mortar should be prepared in small quantity so that it can be consumed before starting of initial setting time of cement.

8. Machine mixing: Machine mixing is adopted when the large scale of mortar is required continuously at a fast rate . Machine mixing is not only efficient but also economical. It is prepared by mixing of the mortar ingredients in mechanical mixtures. It involves following main steps: Predetermined proportion of sand and cement are put into the drum of mixture and then added required quantity of water before revolving the drum. The drum is allowed to revolve continuously for a sufficient period of time (at least for 2 minutes) till a mortar of uniform consistency is obtained. Water in small quantity at a time can be added to achieve uniform and homogeneous mix. The mixed mortar than poured out from the mixer drum for use. It is important to know that poured cement mortar should be consumed before starting of initial setting time of cement.

9. Classification based on bulk density: Based on the bulk density of the mix in dry state, it is of two types: Light weight mortars: This type of mortar is prepared form light weight porous sands from pumice and other fine aggregates. It is also prepared by mixing wood powder, saw dust with cement or lime mortar. The bulk density of this mortar is less than 1500 kg/m 3 . These mortars are used in construction of light weighted structures . Heavy weight mortars: This type of mortar is prepared form heavy quartz and sands. The bulk density of this mortar is more than 1500 kg/m 3 . These heavy weighted mortars are used in load bearing construction.   Classification based on nature of application: Based on nature of application, mortars are classified as follows: Brick laying or masonry mortars: These mortars are used as binding medium between the brick masonry units. Lime mortars, cement mortars, lime-cement mortar, and lime-surkhi-mortar may be used according to nature of construction. Finishing mortars or plasters: These mortars are used as protective covering over walls such as plastering and pointing and also used for creating architectural finishing. Such type of mortars should have strength, water repellant ability, and resistance to atmospheric actions such as rain, wind, dust storm, frost action, freezing and thawing action, atmospheric impurities etc.

10. Special mortars: Mud mortars: This mortar is prepared by mixing clay with water until it comes to the required consistency. Mud mortar is very cheap and the ingredients are locally available. It is a low strength mortar and it is the weakest of all mortar types. The life of this mortar surfaces varies from 5 to 15 years depending on its water proofing treatment and weather conditions. It can be easily scratched from the wall using a sharp object. This type of mortar is mostly used in inferior construction, stone and brick masonry housing construction in remote rural areas where cement or lime are either unavailable or too expensive.   Cement- clay mortars: This type of mortar is obtained by mixing fine powder of clay as additives. It should be remember that the quantity of clay should not exceed limit of 1:1 to cement . The reason behind the addition of clay is not only to increase the density of mortar but also to improve water retaining ability and workability of mortar. It is generally used for masonry joints and plastering.   Decorative mortars: This type of mortar is obtained by using color cements or pigments and fine aggregate of suitable color, texture and surface. These are highly used to provide appealing appearance to the outer as well as inner surfaces of the structures.

11. Air-entrained (plasticized) mortar: The workability and good plasticity of lean cement-sand mortar can be improved by entraining air by including a small quantity of air entraining agent in a mix. This agent helps to produce minute voids in the mixed mortar. The workability of a lean mortar is thus improved and bleeding and segregation are reduced. It also makes the mortar light weighted, improves better heat and sound insulation and increases its resistance to frost action. Sound absorbing mortar: This type of mortar is obtained by using binding materials in the form of cement, lime, gypsum, slag etc. and fine aggregate in the form of light weight porous materials such as pumice, cinders etc. The bulk density of such mortars varies from 600 to 1200 kg/m 3 . This mortar can be used as a plaster to reduce intensity of noise level. Chemical resistant mortar: This type of mortars is prepared from using suitable type of additives to cement-sand mortar to provide resistance against a typical chemicals or group of chemicals. This type of mortar is use for chemical resistant floors, tank lining, drains etc. The silicate type mortar is found to be satisfactory to resist nitric acid, chromic acid, sulphuric acid and hydrochloric acid.

12. X-ray shielding mortar: This type of mortar is prepared by using fine aggregate of heavy rock . Suitable admixtures are also added to enhance protective properties of mortar. The bulk density of such mortar is more than 2200 kg/m 3 . This type of mortar is used for plaster of walls and ceiling of X-ray cabinets.   Packing mortar: This mortar is used to pack oil wells. It should possess the properties such as resistance to sub soil water pressure, high homogeneity, predetermined setting time, high water resistance etc. Commonly used various packing mortars are: cement- sand mortar, cement- loam mortar, cement-sand-loam mortar. (loam: ~ is a specially graded fine sand and clay blend together) Fire resistant mortar: This type of mortar is prepared by adding one part of aluminous cement to two parts of finely crushed powder of fire-bricks. This mortar is used with fire- bricks for lining furnaces, chimney, ovens, fire places etc.

13. 6.4 Selection of mortar for civil engineering works Depending on the nature of various engineering works, suitable type of mortar should be selected with the recommended mix proportion is given in table below.

14. 6.3 Function of mortar : Following are the main functions of mortar in building construction: It provides a binding force or cohesion between the building units such as in stones, bricks or in cement blocks etc. with considerable strength after hardening. It acts as a medium for distributing the incoming loads throughout the structure uniformly. It should act as barrier and provide additional strength to the structure against weathering agencies such as rain, frost action, freezing and thawing action, atmospheric impurities etc. In case of concrete work, it holds coarse aggregates together so as to form a solid mass. It does pointing or plastering to the structure.

15. Properties of mortar : Following are the main properties of mortar in building construction: The mortar mix should have good workability, plasticity and durability. The mortar should be resistant to salt efflorescence. The mortar should be safer for adjacent neighboring materials with which it comes in contact. The mortar should have good setting and hardening properties so that the speed of construction is ensured without compromising in quality of work. The mortar should have long lasting adhesion with masonry units. The mortar should provide strength to the masonry. The mortar should offer good resistance to moisture. The mortar should not develop any cracks on drying. The mortar should be affordable.

16. Uses of mortar: Following are the reasons for which it is extensively used: It is used for binding masonry units such as stones, bricks, hollow cement blocks etc together into a solid mass. It is used to form even and soft bedding layer for masonry units so that it can transfer upward load uniformly to its foundation. It is used for water proofing of roofs. It is used for topping cement concrete floors. It is used for pointing and plastering work on exposed surfaces of masonry. It is used to improve general appearance of structure and neat finishing to concrete works. It is used for hiding open joints of a brickwork and stonework. It is also used for hiding bad workmanship. It is used to fill up cracks detected in structure during the maintenance process, etc

17. 6.5 Tests for mortars (Extra) Following are the tests usually conducted to determine the quality of mortar: Crushing strength test. Tensile strength test. Adhesiveness to building units test.   Crushing strength test: The mortar to be tested is applied uniformly and horizontally on a set of bricks. The brickwork so formed is allowed to set and harden. A sample of this brickwork is taken and it is gradually loaded in a universal testing machine till failure occurs due to crushing. The load at which crushing of the brickwork took place is note down. The crushing strength of the mortar is failed load divided by the area of the mortar. The crushing strength of mortar will depend on: Type of mortar Ratio of mortar mix This will vary between 0.4N/mm 2 for lime mortars to 0.7N/mm 2 for cement mortar.

18. Tensile strength test: For this test, the mortar of standard mix i.e. 1:3 is placed in the mould of briquette as shown in figure 6.1. These briquettes are allowed to set and harden. It has central cross-sectional area as 38 mm × 38 mm or 1444mm 2 . The briquette is pulled under the grips of tensile testing machine. The ultimate load noted down. Then the tensile strength of mortar is failed load divided by the central cross-sectional area. Fig 6.1: Briquette for tensile strength test and briquette mould

19. Adhesive Test: As shown in given figure 6.2, the two bricks are placed at right angles to each other and joined together with mortar to be tested. The upper brick is suspended from an overhead support and the weights are attached to the lower brick. The weights are gradually added to the lower board until the bricks separate. The ultimate adhesive strength of mortar is the failed load divided by area of contact.

20. End of Chap 6