Learning text part 03 - Mortar

1 AggregatesLearning text part 03 Contents pageIntroduction 1 Rock formation 1 aggregate processing 1 Sand and gravel 1 Crushed rock 1 Marine dredged 1 Grading of aggregates 1 Lightweight aggregates 2 Impurities 2 Silt, clay and fines 2 Organic matter 3 Chlorides 3 Sulfates 3 Iron pyrite 3 Lignite and coal 3 Shell content 3 Mica 3 Testing 3 - 4 mia Mortar industry associationMineral Products Association page Handling and storage 5 European standards 5 Glossary of terns 5 Bibliography 6 Self-assessment questions 7 Answers to

2 Self-assessment questions 8 Health and safetyAll Mortar mixtures, both wet and dry, are abrasive and alkaline. When working with wet Mortar , waterproof or other suitable protective clothing should be worn. Guidance on the use of these materials can be found in MIA data sheet No. 20. IntroductionThis Learning text covers the formation, specification and properties of the aggregates used in Mortar . A glossary of terminology used and a bibliography are included while the final section contains self-assessment questions and answers. Sand - sometimes referred to as fine aggregate - is the main constituent of masonry mortars and renders. Some screeds incorporate a coarse aggregate (normally 10mm maximum size) but generally sand is their major constituent.

3 Sand quality is affected by a number of factors: mean particle size grading presence of impurities shape the main constituent of masonry mortars, renders and screeds, sand has a significant effect upon the properties of the product in both its fresh and hardened state. Selection of suitable aggregates, capable of producing a product with the optimum properties, is most important. Design of Mortar mixes is based on the concept that the voids in the sand, which are generally in the range 25-40%, will be filled with binder. Where voids are not completely filled, there is an increasing risk that the Mortar will not be durable. A later Learning text in this series, part 6, Properties of masonry mortars, explains the importance of desirable properties of masonry Mortar , which are influenced by the grading and consequent voids within the formationThe earth is composed of rocks that have been formed over hundreds of millions of years.

4 Its centre is a core of solid material, believed to be made up of nickel and iron. A number of layers, some composed of liquid material called magma, make up the structure of the earth with the outermost layer being called the crust. The earth s crust varies a great deal in thickness ranging from about 65km under mountains, to as little as 5km under some oceans. The crust is the source of rocks used by divide rocks into three categories:to a dewatering system to allow the excess processing water to be alternative to the washing and classification system is to dry screen the extracted material, leaving a product which will have a higher proportion of fine material which may be beneficial in the production of and gravels are normally rounded or irregular in shape.

5 Increasingly some gravels are crushed to produce smaller particles with an angular shape similar to crushed rockCrushed rocks are obtained from a quarry by drilling and blasting the bedrock. The rock is then transported to the processing plant where, after removal of the fine material, it is crushed and screened a number of times before arriving at its selected sizes. Due to the processing requirements, crushed stone is more expensive to produce than sands and dredgedExtraction of marine aggregates is a similar process to the wet process of sand and gravel extraction, except that the suction pump or dredger is located on a ship with a hold capacity of up to 5,000 tonnes.

6 Marine aggregates are extracted from a number of locations around the UK coast. Material is off loaded at wharves and then processed, particular care being taken with washing and draining to reduce the chlorides that are present from seawater. Use of marine aggregates has increased as fewer reserves of land-based materials are available and planning permission for extraction becomes more difficult to obtain. Thus is particularly noticeable in areas such as London where there is good river of aggregatesSands, gravels and crushed stone come in a variety of shapes and sizes and classification of these materials into approximate size fractions is called grading.

7 Traditional terminology was to classify aggregates as Igneous rocks - derived from molten material, which originates from the layers below the earth s crust and is ejected by volcanoes. Some molten material solidifies before it reaches the earth s surface and that is the reason a range of igneous rocks exist, their properties being dependent on the rate of cooling as well as the chemical composition of the liquid magma. Igneous rocks include granite, diorite and basalt. Sedimentary rocks - the majority of these originate as accumulations of material, formed as a result of the transportation of solid particles eroded from preexisting rocks to the place where they are deposited as sediments.

8 Other sedimentary rocks are formed from the accumulation of animal or vegetable remains. A third group is formed from the precipitation of materials carried in solution. Sedimentary rocks include limestone, sandstone and gritstone. Metamorphic rocks - metamorphism is the term used to describe the transformation of rocks into new structures and mineral compositions, as a result of the energy put into them by heat and/or pressure. When fine grained limestone is metamorphosed then the whole mass is recrystallised into marble, coloured bands in the material arising form the varying chemical compositions of the original rocks also include slates and processingSand and gravelSands and gravels are obtained by either a wet or dry extraction the wet process, the main types of equipment used are suction dredgers, floating cranes, floating grab dredgers and draglines.

9 In the dry process the first step is removal of the topsoil or overburden, then a front-end loader or excavator digs out the material which is conveyed to the processing plant. Extracted material is washed in a scrubber at the processing plant to remove clay and silt particles and then screened into its constituent sizes. The fine material passes to a series of classifiers where a process of differential settlement allows various grades of sand to be produced. Material then passes 10 (6) (12) (32) to one of three categories; all in aggregate ; coarse aggregate and sand. These are defined below but it should be noted that the first two categories are not used in Mortar production.

10 All in aggregate : this is material composed of a mixture of coarse material and sand. Coarse aggregate : over 4mm material. This classification can be further divided into graded and single-size aggregates. A graded aggregate consists of particles of different sizes from the maximum down to the minimum. Sand: The European Standard uses the term fine aggregate in place of sand for material less than or equal to 4mm in size but the terms are interchangeable and the word sand more commonly used. The European Standard BS EN 13139 lists the preferred sizes of aggregates for Mortar , these are: 0/1mm, 0/2mm, 0/4mm, 2/4mm and 2/8mm. (Where the first figure in each set represents d and the second D).