CC 203 CONCRETE TECHNOLOGY TOPIC 2 CONCRETE WORKS AT THE CONSTRUCTION SITE Lecturer name:MOHD HAZMAN BIN ABDUL AZIZ
SUB TOPIC 2– Factor that cause of occurrence material segregation and bleeding.– Fresh concrete.– Concept of hard concrete.– Preparation of concrete at site.– Concept of transporting concrete.– Concept of casting and placing concrete.– Method of compaction concrete.– Method of curing concrete.– Standard laboratory testing on concrete mixture.
SUB TOPIC 2.1 Factor that cause of occurrence material segregation and bleeding. - Describe the segregation and bleeding of concrete. - Show the segregation and bleeding of concrete mix. - Effect of segregation and bleeding on quality of concrete.
Segregation Separation of the constituent materials of concrete. Source - low limit of compacting Can divide by 3 types cause : a) Coarse aggregate separating out or settling down from the concrete mix. b) Paste separating away from coarse aggregate. c) Water separating out from the material being of lowest specific gravity.
Bleeding Bleeding in concrete is sometimes referred as water gain It is a particular form of segregation, in which some of the water from the concrete comes out to the surface of the concrete, being of the lowest specific gravity among all the ingredients of concrete. Source – over limit of compacting
Effect of segregation and bleeding on quality of concretee) Strength of concretef) Surface cracking.g) Bonding of material in concrete mix
SUB TOPIC 2.2 Fresh concrete - Relate the workability of wet concrete with water cement ratio. - Testing on workability of concrete a) Slump test. b) Vebe test.
Relate the workability of wet concrete with water cement ratio. One of material in concrete mixture. If volume of water are over limit the strength and density of concrete is reduced. Ifvolume of water are low limit the concrete will be difficult to do and the hydration process is not perfect.
• Slump TestPurpose : To determine the workability of concrete at site. ( BS 1881: Part 102:1983 )Apparatus : Cone dan base plate. Circular tamping rod 12mm. Ruler steel and concrete mixing equipment. Concrete.
Procedure: Prepare materials for the concrete mix according to the mix ratio as directed. Clean the surface of the cone, then lay on a flat base plate. Include the concrete mix into the cone of 3 layers and each layer compacted by 25 times using a tamping rod stuffing until full. Flatten the top and clean the concrete surface. Slowly and carefully remove the cone by lifting it vertically and place the cone next the concrete mix.
Place the rod horizontal at cone and concrete slump. Measure and record the distance slumps the concrete. Repeat the testing with add water cement ratio.
Data result:No. of testing 1 2Mix Ratio 1:2:4 1:2:4Mass of materials ( kg ) 28 kg 28 kgVolume of water ( liter ) 2.3 L 2.8 LHeight of cone ( mm ) 300 mm 300 mmHeight of slumps ( mm ) 275 mm 245 mmDistance of slumps ( mm ) 25 mm 55 mm * Range BS( Limit slump 0 – 150 mm )
b) Vebe test Objective : to determine the workability of fresh concreteApparatus Concrete Vebe consistometer mechine
PROCEDURE i) A conventional slump test is performed, placing the slump cone inside the cylindrical part of the consistometer. ii) The glass disc attached to the swivel arm is turned and placed on the top of the concrete in the pot. iii) The electrical vibrator is switched on and a stop- watch is started, simultaneously. iv) Vibration is continued till the conical shape of the concrete disappears and the concrete assumes a cylindrical shape. v) When the concrete fully assumes a cylindrical shape, the stop-watch is switched off immediately. The time is noted.
SUB TOPIC 2.3 Concept of hard concrete. - Criteria of hard concrete a) Compression strength b) Tensile / bending strength c) Durability ( Ketahanlasakan ) d) Permeability ( Resapan ) e) Resistant to chemical reaction f) Changing of shape g) Shrinkage h) Creeping ( rayapan ) i) Fire resistant
a) Compression strength Most important property of hard concrete. Generally considerad for the design. For ordinary construction compressive strength in a range of 20-40 MPa. Low range (cast in-situ), High range (precast) Testing concrete prepared in standard cube 100 or 150mm for 7,14,21 and 28 days.
b) Tensile / bending strength. Should be high to resist cracking from shrinkage and temperature changes. Measured using one or more for i) Direct tension test ii) Split cylinder test iii) Flexural test.
c) Durability ( Ketahanlasakan ) Concrete should be design to serve its purpose Factors that influence durability can be divided into: – the environment and usage factors (outside control) – the composition and production factors
d) Permeability ( Resapan ) The low permeability of concrete is essential to increase the resistance properties of cooled action, chemical action and protects the place of steel corrosion occurs. To obtain a low permeability, the concrete should be fully compressed and the preservation of good done. Permeability can also be reduced by using water content and increase the cement content.
e) Resistant to chemical reaction Portland cement concrete is often attacked by acids such as organic acids and other food processing, especially when the work performed. Chemical elements are commonly attacked concrete sulphate salt present in the soil and in sea water. Resistance properties of concrete sulphate attack depends on the type of cement used, the cement content and water cement ratio.
f) Changing of shape Elastic deformation that occurs at that time and depending on the value of applied stress. Drying shrinkage that occurs in a long time and does not depend on the stresses in the concrete. Creep occurred in the long run, but depending on the value of the stresses on the concrete. As other materials, the concrete will also experience expansion and contraction due to temperature changes.
g) Shrinkage Shrinkage of concrete depends on the amount of drying that occurs. Thus it is affected by humidity and ambient air temperature, air flow rate on the surface and the rate of surface area and volume of concrete. In normal conditions, contraction was influenced by the amount of available water in the concrete during the mixing and the cement content. For a small concrete, usually assumed that half of the drying occurs in one of the first month and the balance within six months thereafter.
h) Creeping ( rayapan ) Creep of concrete depends on the value of the stresses in it. For stresses up to 1 / 3 of the cube strength is considered to be directly proportional to the creep stress. Creep is affected by temperature and moisture environment, the cement content in concrete, water cement ratio, cement type and nature of aggregates. The mass of concrete also has some influence on the creep, but much less than its effect on contraction. The parameters used to evaluate the creep is the ratio of applied stress on concrete cubes at one point of time.
i) Fire resistant The combustion temperature is below 400[degrees] F (200[degrees] C). At this temperature, only the free water in the concrete will be lost, and the strength loss is minimal. Mineralogical changes in hydrated cement occur at higher temperatures. The most important factor is consider is the selection of aggregate. The differential thermal movement between the cement paste and the aggregate is what can cause damage. Quartzite aggregate is the most prone to fire damage by cracking through the quartzite aggregate and bond failure between the cement paste and the aggregate. Limestone aggregate exhibits better fire resistance when exposed to low temperature fire. Lightweight aggregate also performs well. For this situation, a 6 1/2-sack lightweight concrete should provide all the heat resistance needed. At higher temperatures (above about 800[degrees]F), high-heat-resistant concrete is generally needed. Light-weight aggregates have proven to be more heat resistant and so that is the first step--use lightweight. When temperatures get extremely high, above 1000[degrees]F, calcium aluminates cement produces a fire-resistant concrete.
SUB TOPIC 2.4 Preparation of concrete at site. - The batching method of concrete. a) Volume method. b) Weigh method. - The mixing method of concrete. a) Manually. b) Machinery.
The batching method of concrete. a) Volume method. using the measuring box and the conventional method, which has long been used to work at construction site. This method can not be used for work that requires accuracy because of the volume of concrete depends on its density. The ratio of each substance is calculated based on the volume of concrete. volume of cement is calculated based on the volume of one bag / weight of cement and sand as well as for coarse aggregate measured by volume of the same bag
Density of cement ( BS = 1442kg/m2 ) to determine the measure of box : 1bag cement = 50kg/ 1442kg/m3 = 0.035 m3 The measuring of box is ( 0.33m x 0.33m x 0.33m = 0.035m3 )
b) Weigh method. using the principles of the scales. suitable for control purposes in the laboratory for testing purposes.Example:Mix ratio (1:1.9:3.8 ) and W/C = 0.51 bag cement x 50kg = 50kg1.9 x 50kg fine agg. = 95kg3.8 x 50kg coarse agg. = 190kgVolume of water = 25L
The mixing method of concrete.a) Manually. Mixing by hand. Can’t to used or efection for the high workability. Mixing for are small quantity mixture.
b) Machinery.i )Types T – drum are lean This machine are used drum for mixing the materials of concrete. When mixing are finish the concrete will be throut. The shape of machine is cone and spin in one direction. The angle of casting is 400 to 600 .
ii )Types NT – drum are not lean ( Cylinder ) This machine shape like cylinder and same are machine Types T. The drum spin in vertical part. The concrete mixing well throut at bottom part of machine.
SUB TOPIC 2.5 Transporting method of concrete. - Defination of ready mix concrete. - Transporting method of concrete on site. a) Wheelbarrow. b) Chute. c) Pump. d) Crane.
Ready mix concrete Ready-mix concrete is a type of concrete that is manufactured in a factory or batching plant, according to a set recipe, and then delivered to a work site, by truck mixers.
Transporting method of concrete on site.a) Wheelbarrow Used for concrete transporting in small quantity. Used to transport the concrete materials such as cement and aggragate.
b) Chute. Tools to transporting concrete from heigth to the lower place. Made from PVC pipe , wood and other materials. Chute limited for 3m and diameter is 300mm.
c) Pump. fast method and economical if careful planning. using pipe ɸ 6” to pumped from the mixing place. used for large quantities concrete. can carry as long 30m – 50m vertically and 300m – 500m horizontal direction. have two type is plunger pump and press pump. used in difficult to utilise lorry and trasport machine.
d) Crane. Have two types: i) mobile crane. ii) tower crane.i) Mobile crane Used for project large and in the construction of high structures less than 30m. The concrete include in large container have a trap door at bottom.
ii) Tower crane Used for building higher than 30m Use skrip depend on load of size Size of skrip is 1394kg @12.57m3 If the concrete placing is high, a large of skrip should be used to make it more economical.
SUB TOPIC 2.6 Casting and placing of concrete. - Method of casting and placing for concrete. - Procedures of casting and placing on site.
Method of casting and placingCasting Space to casting the concrete in formwork at each structure member much be less than 1.2m for avoid the segregation cause. Must be casting the concrete layer by layer.Placing Must be placing early after mixing with water. Maksimum times is 11/2 hour.
Procedures of casting and placing on site. Concrete mix must be near at site. Must be placing in a uniform layer by layer for avoid separation materials. For structure concrete wall and column must be placing in layer thickness 450mm. Concrete must be quickly as possible to prevent from hardening. Make sure every layer must be compact before the next layer. Avoid for cold joint. Avoid bar reinforcement move during the
SUB TOPIC 2.7 Compacting method of concrete. - Method of compacting for concrete. a) Steel rod. b) Vibrator machine. ( internal , external and platform ) - The advantages and disadvantages of compacting concrete using vibrator and steel rod.
Method of compacting for concrete.a) Steel rod Using for laboratory testing. Diameter steel rod 12mm.
b) Vibrator machine. (internal , external and platform)Internal vibrator Widely used by electric or diesel power. Compaction of this type has different sizes of vibrating pins 10mm to 25mm. Must be done carefully so that the reinforcement in the mold is not move or damaged.
Platform vibrator is a table supported by a number of springs that run by electricity which allows the face of the vibrating table. usually used in workshops to make the precast concrete. Concrete parts shall be made in formwork and placed on the table to vibrator for compact.
The advantages and disadvantages ofcompacting concrete using vibrator andsteel rod.
SUB TOPIC 2.8 Method of curing concrete. - Purpose of curing. - Method of curing concrete. a) Covered with wet materials( sacks, plastic, wood dust ) . b) Flooding or spraying with water. c ) Sweeping with chemicals. d ) Using a vapor steam.
Purpose of curing. Prevents the loss of water from the concrete during the hardening process. Avoid loss of water from the concrete. Can control the temperature of concrete. Can guarantee a hard surface, compact to avoid the risk of cracking. Can prevent the bleeding.
Method of curing concrete.a) Covered with wet materials( sacks, plastic, wood dust ). Covered with sacks wet, plastic,wood dust, sand, and other wet materials. Materials that may damage the color of concrete can not be used.
b) Flooding or spraying with water. Flooding or spray on the concrete surface with water. This method is suitable for concrete work on the floor.c ) Sweeping with chemicals. Sweeping chemicals such as silica compounds in the concrete surface to prevent water loss from evaporation.
d ) Using a vapor steam. This method is used in the factory to accelerate the curing process, especially for pre – stressed concrete.