QUESTION 1 [ 20 MARKS] Complete the following statements. Note that you are allowed to ONLY use terms from the list below; other terms WILL NOT be accepted. ( 10 MARKS) The appearance of water along with cement particles on the surface of the freshly laid concrete A measure of how well concrete will handle freezing and thawing, wetting and drying, and physical wear. The ability of a hardened cement paste retain its volume after setting without delayed destructive expansion The property determining the effort required to manipulate a freshly mixed quantity of concrete with a minimum segregation The ability of fresh concrete to hold all the ingredients together uniformly
List of possible terms:
Consistency, Compactability, Soundness,
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(10 MARKS) Fineness Modulus (FM) is computed by adding the cumulative percentages of aggregate passing on each of the specified series of sieves, and dividing the sum by100. For ensuring quality of concrete, use single sized aggregates. The bulk density of aggregates does not depend upon size and shape of the container. The increased cohesiveness of concrete makes it more liable for surface scaling in frosty weather. The commonly used material in the manufacture of cement is sand stone. Angular aggregate increase the void content. Presence of moisture in sand causes an additional problem called “damping”. The purpose of concrete compaction is to increase the weight of concrete. The shrinkage of concrete is due to change in cross-sectional area. Rounded aggregate gives maximum ratio of surface area to the volume.
QUESTION 2 [ 20 MARKS] Fill in the blanks (10 marks) Concrete is …………………………………………………………………
[A]Cement [B] Cement paste [C] Cement paste & Fine aggregates [D] Mortar & Coarse aggregates.
The process of keeping the concrete structure moist is called ……………………….. [A] Hydration [B] Curing [C] Creep [D]
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[A] Slightly acidic [B] Free from bacteria [C] Distilled [D] Potable. The process of proper and accurate measurement of concrete ingredients for uniformity of proportion, is known as ……………………………………… [A]Curing [B] Mixing [C] Grading [D] Batching.
The length of time for which the concrete mixture remains plastic predominantly depends on the …………………………………………………
[A]Setting time of cement [B] Amount of mixing water [C] Atmospheric temperature. Generally the strength of concrete is represented by the crushing stress of concrete cube of size ……………………………….. [A] 50 mm [B] 100 mm [C] 150 mm [D] 250 mm. An aggregate is said to be flaky, if its least dimension is less than…………………. [A] 2/3 mean dimension [B] 3/4 mean dimension [C] 3/5 mean dimension [D] 5/8 mean dimension. The continuous strain, which the concrete undergoes due to application of external loads is called………………………………………. [A] Creep [B] Bleeding [C] Workability [D] Segregation. Workability of concrete mix with low water cement ratio is determined by ………………………………… [A] Tensile strength test [B] Slump cone test [C] Compaction factor test [D] Flexural strength
they're not. Concrete is to cement as a cake is to flour. Concrete is a mixture
concentrations of 10mM, 20mM and 40mM. What this finding tells us is that our manipulation
Weigh a clean and dry small beaker to the nearest 0.01 g or whatever value is possible. Record its mass in grams. Pour the contents of the graduated cylinder into the beaker. Weigh the beaker and water. Record the mass.
Checking the opening of cracks and stress limits, will not be required for concrete elements. When the tensile flexural stress exceeds the effective tensile strength fcteff, then a check for pre-stressed concrete is required. This should normally occur when sections do not have tendons near the tension face or there is no exposure to chlorides, so decompression doesn’t have to be checked. The analysis using uncracked section will be done in sections controlled for decompression and have tendons near the surface tension. As the cracked section analysis is done by computer, it solves the complexity of the calculations. However, this does not mean that pre-stressed cannot be calculated directly from a set of equations as with crack width checks for RC.
Finished cement is pumped pneumatically to storage silos from which it is drawn for packing in paper bags or for dispatch in bulk containers.
In figure (2.26), eight equations proposed by different researchers have been plotted for lightweight concrete, as shown in table (2.12). The experimental splitting tensile strength values are calculated as follows: Eq. (2.23), (2.24), (2.25) (2.26) for cube specimens and (2.27), (2.28), (2.29), (2.30) for cylinder specimens. The splitting tensile strength of lightweight concrete for Eq. (2.23) ranged from 2.8 – 3.5 MPa, as shown in figure (2.23).
Concrete is a composite material used widely in the construction industry. Concrete is basically a mixture of cement, water, aggregates and admixture (sometimes). Cement is a fine gray powder that consists of oxidizes calcium, silicon and aluminum. The aggregate used is normally gravel, crushed stone or sand. Admixture is a solid or liquid substance that gives a certain characteristics of the concrete. The cement reacts with water chemically and binds the aggregates together through a process called hydration during hardening or curing of concrete. It means that water helps in the hardening of the concrete while the cement bind the aggregate and also react with water to form a solid mass.
Gravels constitute the majority of coarse aggregate used in concrete with crushed stone making up most of the remainder. Angular aggregate increase the void content. Larger sizes of well-graded aggregate and improved grading decrease the void content. Absorption and surface moisture of aggregate are measured when selecting aggregate because the internal structure of aggregate is made up of solid material and voids that may r not contain water. The amount of water in the concrete mixture must be adjusted to include the moisture conditions of the
To determine the grain size distribution of material passing the 75m sieve the hydrometer method is commonly used. The soil is mixed with water and a dispersing agent, stirred vigorously, and then allowed to settle to the bottom of a measuring cylinder. As the soil particles settle out of suspension, the specific gravity of the mixture reduces. One hydrometer is used to record the variation of specific gravity with time, Figure 4.2. By making use of Stoke’s Law, which relates the terminal velocity of a free falling sphere to its diameter, the test data is reduced to provide particle diameters and the % by weight of the sample finer than a particular particle size.
Cement is a finely ground compound of limestone and clay or marl (Chandigarh, 2001). It is used in hydraulic binding since it hardens and binds together aggregates and becomes waterproof thereafter. The most popular use of sand is in building and construction where it is used to bind sand and gravel to obtain concrete used in constructing houses, roads, water channels, among others. Yanbu Cement company produces different types of cement such as Portland cement types I, II, III and IV.
Formwork is a model including all supporting structure, used shape and support the concrete until it attains sufficient strength to carry its own weight. It should be possible of carrying all imposed dead and live load apart from its own weight.
Opus caementicium or Roman concrete is a synthetic construction substance that’s composed of an aggregate, a binding agent, and water. In Rome’s case, as discovered by UC Berkley with the extensive analysis of a sample of Roman concrete taken from a breakwater in Italy’s Pozzuoli Bay it was developed by using lime and volcanic rock which formed a mortar, the mortar and volcanic rock were then packed into wooden forms and when seawater was added a chemical reaction occurred, bonding everything together to create concrete (History, 2013). It is uncertain when Roman concrete was developed, but it was clearly in widespread and customary use from about 150 BC; some scholars believe it was developed a century before that.
Concrete The term concrete is derived from the Latin word “concretus”, which means to grow together (National Institute of Standards and Technology, n.d.). Opus caementicium or the Roman concrete was developed in the 2nd BCE. Mortar was a mixture
The science of mixing the ingredients to make concrete is called mix design. The selection of mix proportions is thus, simply, the process of choosing suitable ingredients of concrete and determining their relative quantities with the object of producing as economically as possible concrete of certain minimum properties, notably strength, durability, and a required consistency. It can be seen then that mix selection requires both knowledge of the properties of concrete and experimental data or experience.
This paper evaluates the effect of heat on the compressive strength of concrete by way of comparing the strength of concrete that is subjected to heat treatment with unheated one. Concrete ingredients available locally were obtained for the production of concrete cubes into a dimension of 15x15x15 cm. A total of 12 cubes were casted and then cured at room temperature (28 °C). The cubes were divided into 4 sets. Each set comprised of 3 cubes for each Water-Cement ratio. Two of these sets were cured for 14 and 28 days out of which one set each was heated at a temperature of 200oc for about 4 hours. They were then crushed subsequently to compare their strength. The results revealed that at the 14 day curing, the average compressive strength for