What is Construction Material Engineering?

Civil engineers are often responsible for specifying, designing and manufacturing the materials with which they build their structures. Studies in construction materials are intended to make structural, transportation and foundation engineers aware of the fundamental properties of the materials they us.

Concrete Core drilling and preparation of samples for Compressive Strength test

Cores are cut using a drill with a hollow barrel tipped with industrial diamonds. The whole rig has to be firmly fixed in position by weights, anchor bolts, vacuum pads or bracing against other parts of the structure. The preferred core diameter for strength testing is defined in BS EN 12504-1, BS EN 13791 or BS 6089 but the diameter should be at least 3.5 x the maximum aggregate size.  Sometimes even smaller diameter cores have to be used for strength testing. In this case the strength results can be more variable and a greater number of cores should be extracted. For strength testing, the length to diameter ratio should be between 1 and 2 and preferably between 1 and 1.2. When cores are received in the laboratory they may be examined for degree of compaction, cracks, voids, honeycombing and the presence of reinforcement.

Before testing cores for strength, they have to be trimmed to length and the ends prepared so that they are flat and perpendicular to the longitudinal axis. This is achieved by grinding or, more usually, capping with high alumina cement (calcium aluminate cement) mortar or a sulphur/sand mixture. Cores should be tested in a dry state. This is a air dry, not oven dry. If tested wet a small positive correction to the strength is made.

Los Angeles abrasion and aggregate grading

The Los Angeles (L.A.) Abrasion Test: is a common test method used to indicate aggregate toughness and abrasion characteristics. Aggregate abrasion characteristics are important because the constituent aggregate in HMA must resist crushing, degradation and disintegration in order to produce a high quality HMA.The standard L.A. abrasion test subjects a coarse aggregate sample (retained on the No. 12 (1.70 mm) sieve) to abrasion, impact, and grinding in a rotating steel drum containing a specified number of steel spheres.

After being subjected to the rotating drum, the weight of aggregate that is retained on a No. 12 (1.70 mm) sieve is subtracted from the original weight to obtain a percentage of the total aggregate weight that has broken down and passed through the No. 12 (1.70 mm) sieve. Therefore, an L.A. abrasion loss value of 40 indicates that 40% of the original sample passed through the No. 12 (1.70 mm) sieve.

Aggregate Grading: is the particle-size distribution of an aggregate. The grading determine the paste requirement for a workable concrete since the amount of void requires needs to be filled by the same amount of cement paste in a concrete mixture. The grading is determined by a sieve analysis using wire mesh sieves with square openings.

Tensile Strength of steel

The tensile strength of a material is the maximum amount of tensile stress that it can take before failure, for example breaking. There are three typical definitions of tensile strength

1-Yield strength - The stress a material can withstand without permanent deformation. This is not a sharply defined point. Yield strength is the stress which will cause a permanent deformation of 0.2% of the original dimension.

2-Ultimate strength - The maximum stress a material can withstand.

3-Breaking strength - The stress coordinate on the stress-strain curve at the point of rupture.

Tensile strength machine

Flexural and compressive strength test

Flexural strength, also known as modulus of rupture, or bend strength, or transverse rupture strength is a material property, defined as the stress in a material just before it yields in a flexure test. The transverse bending test is most frequently employed, in which a specimen having either a circular or rectangular cross-section is bent until fracture or yielding using a three point flexural test technique. The flexural strength represents the highest stress experienced within the material at its moment of yield. It is measured in terms of stress.

Compressive Strength, is a very common testing method that is used to establish the compressive force or crush resistance of a material and the ability of the material to recover after a specified compressive force is applied and even held over a defined period of time. Compression tests are used to determine the material behavior under a load. The maximum stress a material can sustain over a period under a load (constant or progressive) is determined.