NATIONAL CERTIFICATE (VOCATIONAL) NQF LEVEL 2 SUPPLEMENTARY EXAMINATION

Transcription

1 MARKING GUIDELINE NATIONAL CERTIFICATE (VOCATIONAL) NQF LEVEL 2 SUPPLEMENTARY EXAMINATION 2010 This marking guideline consists of 6 pages.

2 (MARKING GUIDELINE) -2- NC1530(E)(F19)V QUESTION 1: INTRODUCTION TO False False (4) 1.2 Aggregate are any loose materials such as sand, gravel or pebbles, that is added to a cementing agent to make concrete and plaster Stress is the results of a force over an area. Tension is the stress created when an object is pulled at People are protected from harmful materials. - Trade with other countries is boosted. - When writing contract specifications refer to various SANS documents. - Standards allow the control of materials and procedures in terms of quality. - Any One = 1 x It can always be used without running out - Exploitation, processing or use of a particular material or process will not harm the environment - It is a material that future generations will be able to use. Any TWO 2x ½ To build building using materials that have low energy requirements - It requires very little energy to run and to maintain. Any ONE QUESTION 2: BASIC GEOLOGY CONCEPTS Galactic nebula is a cloud of gas and dust in space, found in our milky way. Orbiting is moving around a large object on an elliptical or oval path The core - The mantle - The crust (3)

3 (MARKING GUIDELINE) -3- NC1530(E)(F19)V River sand - Pit sand - Dune sand - Beach sand - Crusher sand Any THREE (3 x 1) (3) QUESTION 3: SOIL AND EARTH AS A FOUNDATION AND BUILDING MATERIAL 3.1 Impact tamper Hand vibrator Plate vibrator (3) 3.2 Adobe has been used to construct buildings for about the past 8000years. It is generally accepted that arches, domes and vaults were firstly developed in the middle east. Adobe is a building method that is still widely used in the Middle East and around the Mediterranean coastline. Adobe also has a long history in South and North America. refers to the mud from which the bricks are made with other materials being added later like animal dung and straw. Any THREE (3) Compaction is a process that forces the soil particles closer together thus reducing the voids or spaces in the soil. Backfilling is to take accumulated material and refilling a hole that has been dug. QUESTION 4: MASONRY UNITS (BRICKS AND BLOCKS) Face brick extra. Face brick standard. Non-facing plaster. 4.2 Vanadium staining can be seen as a yellow-green discolouration on the brick surface. as a result of water soluble vanadium salts are present in the clay that the bricks were made from cause the stain to appear. 4.3 Mortar smears are smudges of mortar left on the surface of the bricks and lodged in the rough surface and crevices of the bricks.

4 (MARKING GUIDELINE) -4- NC1530(E)(F19)V 4.4 Solid bricks Cellular bricks Hollow bricks. (3) 4.5 Shell bedding is a continuous strip of mortar laid to coincide with the outer shell of hollow block masonry units. 4.6 Slag- is a waste product of the iron making process Clinker.-is a waste product that occurs in the production of cement Crushed burnt clay-is a waste product from the brick making process Bunker ash.-is a by-product of the coal-fired heating process. Any THREE (3) [15] QUESTION 5: CEMENT AND CONCRETE 5.1 Bad design Poor workmanship Applying the concrete incorrectly. Any ONE 5.2 In-situ concrete is concrete that is cast or placed where it is to be used 5.3 The chlorides in the seawater causes accelerated rusting of any steel embedded in the concrete 5.4 Clay and lime are processed and combined with water to form a slurry. this slurry is fed into a rotary kiln, from top to the bottom. Heat is provided by a burner at the lower end with a temperature of 1450 c. at the burner to approximately 70º c at the higher end The slurry is then fed into the kiln at the higher end In this process, all the water will evaporate. The lime will form calcium oxide and combine with the silica from the clay to form dark grey nodules called Portland clinker The fine powder is made from clinker to form Portland cement. The clinker is then ground to a fine powder to form Portland cement Any FOUR (4)

5 (MARKING GUIDELINE) -5- NC1530(E)(F19)V Sand with high fines or clay. - Sugar. - Fertiliser. - Seawater. - Urine. Any THREE (3) 5.6 The purpose of a slump test is to determine the consistency of concrete Permeability. - Strength. - Abrasion resistance. - Freeze-thaw resistance. Any THREE (3) Plasticisers are water-reducing admixers that allow you to decrease the water content of concrete. Retarders is admixture that slow down the hydration of cement initially. Common cement is a cement used for making concrete, and also for mortar. Masonry cement is a cement which is only to be used for making mortar or plaster. 5.9 Concrete is a mixture of sand, cement, crushed stone and water. [25] QUESTION 6: MORTAR 6.1 Mortar binds bricks and blocks together to give strength. It give stability to wall. Mortar forms a dense barrier once it has been placed. Used to bond masonry together Any THREE (3) 6.2 Pre-soaking burnt clay must be wetted for 24 hours before laying so that the sucking of water will be controlled. Dry-laid concrete bricks should not be wetted you should lay it, as dry as it is as it reduces the potential shrinkage of the masonry units 6.3 Floating is to make the surface smooth or level Weak mortar is a mortar with a low cement content. Its role is to supplement the fine aggregate of sand by adding to the very fine factions or particles.

6 (MARKING GUIDELINE) -6- NC1530(E)(F19)V QUESTION 7: PLASTER 7.1 Plaster is used to improve resistance to water penetration. It is used to improve the aesthetics of the walls final. 7.2 High water retention High plasticity High bonding power Any TWO 7.3 Generally plaster which is batched must be used within two hours Hydration would have advanced to a setting stage if not used within the two hours Plaster will crack if used after the optimum two hour period if applied Any TWO 7.4 The substance must be dust free. Texture and water absorption must be assessed. Always check flat and even with a spirit level. Any TWO 7.5 Use rough formwork Strip formwork early and wire brush it Hacking Abrasive blasting Applying a spatter dash layer Any TWO QUESTION 8: SCREED AND TOPPING 8.1 1:4 8.2 Topping is used to provide a dense, abrasion-resistant surface on a concrete base. It increases the structure depth and strength of a base. 8.3 Wet the area on which the new screed or topping is to be laid. Remove all free water from the surface. Allow the concrete to become surface-dry before the slush is applied. (3) False (4) TOTAL: 100