Question

3. Question Three a) State and explain Abram's law (also called the 'water-cement ratio' law) as a concept in civil engineering. Illustrate with the aid of the graph. (5 marks) b) What is gradation of aggregates and explain the importance of proper gradation in fresh concrete? (3 marks) c) Describe the types of shrinkages that concrete undergoes. (6 marks) d) Define concrete mix design and state its benefits. (3 marks) e) Explain the defects in timbers caused by conversion. (4 marks) f) Explain the two basic types of fasteners used in structural steel construction, giving advantages and disadvantages. (4 marks) PI

Answer 1

Dupf Abram's law; " For plastic mixtures using neat and clean aggregates the strength of concrete under specified conditions is governed by the met quautety of water mixed ber bag of cement. Strength of concocte=s= 4 l 5- strength at 28 days, A= 14000 lb/sg.in. Ee B=7 Strength depends only upon wl ratio provided the mix is workable Free w ater in discontinous capillary pares Free water in conten Jous capillary Pares Rates of volume to initial volume cement. Overall volumed tenent past Hydrated cement Paste Unhydrated cement 02 0.4 0.6 0.8 10 water cement ratio & 10 Gel space ratio. Composition of portland cement aste of tor hydration has ceased.

Grading: Distribution of parteces of different sizes in a soil mass is called Gradation of aggregates. Importance Grading has great influence on workability: very fine & coars and have been found to be unsatisfactory for making mortar & concrete. very fine sand - poor mortay Very coarse sand harsh mix. If well graded which consists of different size of particles voids can be minimized. @ Shoinkage typer: 1. plastic shoinkage. 2. Doy shrinkage. 3. Autogeneous shrinkage. 4. carbonation. 1. Plartic shrinkage - It occurs soon after the concrete is placed in formwork, me aus in plastic stage. 2. Doy shrinkage withdrawl of water from - handoned concrete stored in unsaturated air develops dig shrinkage 3. Autogenous shrinkage: Occurs when no movement of water to or from the set paste of concrete is allowed. caused by loss of water at hydration

Mix design: Rational propostioning of ingredients of concrete is essence of concrete mix design. It ensure the most optimum proportions of constituent materials to meet the requirements of strucion being buil It is most economical, efficient to carry, and comply durability and specification requirements. e Defects due to conversion Conversion is the term used to describe the process whereby the felled tree is converted into marketable size of timber conversion defects are basically due to unsound practice in milling on attempts to economice during conversion of timber. A wam occurs in timber which contains, on one or more faces, park of bark or rounded periphery of trunk. This reduces cross sectional area, consequent reduction in strungth in parts affected. Excessice slope of grains may also be classed as conversion defect when conversion has not been done parallel to ans of trunk.

f) Bolts: Advantages: 1) less noise pollution. 2) No need of heating 3) Removal of installed rivets is easy. 4) Inspection of connection is easy. welded connections: adroutages: 1) Structures are lighter. 2) welding prouss quicker 3) mor adaptable than bolting or riveting 4) To achieve 100% percent efficiency 5) Noise produced es relatively less 1) Good aesthetic appearance 1) Joints are rigid 8) Alternations in connections - Disadvantages - 1) It is likely to distort dur un even heating & cooling. 2) possibility of brittle fracture 3) Fails earlier than a botted joint 4) Inspection is difficult 5) Joints are over rigid.