CMT Module 2 Flashcards
FACTORS IN CHOOSING THE PROPER MATERIAL FOR A STRUCTURE
Aesthetic Conditions - Texture, Color, Interaction with light, etc.
Climatic and Cultural Conditions - Humidity, Temperature, Regional and Local Cultural Conditions, etc.
Economic Factors - Raw Mats, Transportation Impact, Costs, etc.
Properties of Material - Mechanical and Non-Mechanical Properties
Construction Consideration - Occupancy, Size of building, durability, structural and fire protection requirements.
Overview of the Building Material Selection Criteria
Strength, Rigidity and Durability (Property of Material)
Environmental Requirements
Economy and others
Structural Characteristics
Density – mass of a unit volume of a material; it can be obtained by dividing the total mass by its total volume.
Specific Weight – also known as the unit weight; this is the weight per unit volume of material.
Porosity – also known as void fraction; measure of the void (hollow space) in a material.
Physical Properties
Moisture – this is the content of water contained in a material.
Thermal Conductivity – this pertains to the ability of material to carry out heat.
Thermal Expansion – this pertains to the expansion or contraction of the material as the temperature changes.
Viscosity – it is the resistance of a fluid which is being deformed by either shear or tensile stress.
Mechanical Properties
A measure of a material’s ability to resist a variety of mechanical forces.
Resistance to applied loads (stress) initially and over time.
Strength – this pertains to the behavior of a material, specifically solid objects, which experiences stresses or strains.
Stress-Strain Relation –
Elastic Behavior – this is the ability of the material to deform when external force is applied and to return to its original state when the stress is eliminated.
Modulus of Elasticity - this is a proportional constant between stress and strain. It is defines stiffness and rigidity of a material, governs deflections and influences buckling behavior.
Ductility – this is the ability of the material to experience large amount of deformations without breaking before failure.
Tensile Stress - this is created when forces pull on a member and tend to increase its length.
Compressive Stress - this is a push (compress) on a member and tend to shorten it.
Shear Stress - produce forces that work in opposite directions parallel with the plane of the force, causing adjacent parts of a material to slide past one another.
Permeability - the rate the water flows through a material. Unit: Perm typically referred to as the perm rating; ex. a vapor retarder is defined as a material having a perm rating of 1.0 or less.
Hardness - this is a measure of the ability of a material to resist indentation or surface scratching. It is the result of several properties of a material, such as elasticity, ductility, brittleness and toughness.
Impact Strength - this is the ability of a material to resist a very rapidly applied load, such as the strike of a hammer. It is an indication of the toughness of a material. A material with high impact strength will absorb the energy of impact without fracturing. It is affected by strength and ductility.
Fatigue Strength - this is the resistance if a material to a cyclic load, one that varies in direction and/or magnitude. This is illustrated by bending a wire back and forth until it breaks. Most materials are lower in fatigue strength than they are in tensile strength. Failures due to fatigue stress occur slowly, and most materials that fail due to fatigue offer some useful life before failure. This is an important factor to consider when the useful life of a product is established.
Stress-Strain Relation
if no external force is being applied to an object or material, this can be considered as an equilibrium position as all its components are in place. Otherwise, this material will exert an effort to go back to its equilibrium or initial position. Technically, this is how you can understand the meaning of Stress. It can be calculated by dividing the external force applied by the cross-sectional area of the material. While the material is experiencing Stress, it undergoes deformation. This is where we can correlate Strain to Stress. Strain is the measurement that shows the change in length of the material divided by its original length.
Yield Strength – it is the maximum stress limit of a material wherein it cannot return to its original shape.
Ultimate Strength – this is the maximum stress that the material can take before breaking; also known as tensile strength.
Other Properties
Thermal Properties
are those that are related to the material’s response to heat. When a material is subjected to a change in temperature it may expand, contract, conduct or reflect heat.
Insulators, Conductors, Thermal Conductivity (k), Thermal Conductance (c), Composite Thermal Performance, Change of State, Heat Capacity
Acoustic Properties
is that branch of physics that deals with the generation, transmission and control of sound waves. It considers the ability of a material to either absorb or reflect sound waves within a room. The acoustical properties of interior finish materials directly affect occupants by influencing the quality of speech, music, and other audio sounds projected in a space. Acoustical materials that perform well as sound absorbers include soft materials such as fabrics, rigid but soft materials, and rigid but hard materials that have the exposed surf ace perforated with holes or slots of varying sizes and placement,
Chemical Properties
Potential reaction with environment
its tendency to undergo a chemical change or reaction due its composition and interaction with the environment. A chemical change can alter the original composition of material and thereby affect its properties.
CLASSIFICATION OF AGGREGATES
- Classification according to Source:
Natural Aggregates
Crushed Rock Aggregates
Artificial Aggregates
Recycled Aggregates – these are aggregates from construction or demolition waste.
- Classification according to Unit Weight
Since aggregates vary, its density and unit weights also have discrepancies. The table below shows the different classifications of aggregates:
Classification according to Size
Fine Aggregates – these are aggregates that pass a 4.75 mm sieve.
Course Aggregates – these are aggregates that are retained on a 4.75 mm sieve.
Classification according to Unit Weight
Ultra-LightWeight - ceramic,
Lightweight - x < 2.4, Clay, Crushed Brick, Slate, Shale
Normal Weight - 2.4 < x < 2.8, Crushed Limestone, Sand, Crushed Recycled Concrete
Heavy Weight - x > 2.8, Steel, Iron Pellets, Iron Shot
MANUFACTURING PROCESS OF NORMAL AGGREGATES
Step 1: Supply
The following are the three major sources of aggregates:
a. Unconsolidated (loose) rock – materials which were formed from clay, silt, sand, and gravel left by flowing streams like river.
b. Solid Rock – materials like limestone or volcanic rock
c. Recycled Materials – materials from actual construction (e.g. demolition works)
Step 2: Extraction
In this step, certain selections or choices are being made like for color or hardness as it can make a huge difference in the appearance of the aggregates.
Step 3: Crushing, Grinding, Screening
Once extraction is done, materials are transferred to the processing site for scalping. This is the process of shaping the stones to various sizes.
MANUFACTURING PROCESS OF LIGHTWEIGHT AGGREGATES
In order for you to produce lightweight aggregates, raw materials are lengthened to about two times the original volume of it. Having said that, material will be less dense. Hence, the lighter concrete material.
Mining or quarrying the raw material.
The material is crushed with cone crushers, jaw crushers, hammer mills, or pug mills and is screened for size. Oversized material is returned to the crushers, and the material that passes through the screens is transferred to the storage.
From the storage, the material is fed to a rotary kiln, which is fired with coal, coke, natural gas, or fuel oil, to temperatures of about 1200°C.
As the material is heated, it liquefies and carbonaceous compounds in the material form gas bubbles, which expand the material; in the process, volatile organic compounds (VOC) are released. From the kiln, the expanded product (clinker) is transferred by conveyor into the clinker cooler where it is cooled by air, forming a porous material.
After cooling, the lightweight aggregate is screened for size, crushed if necessary, stockpiled (storage), and shipped.
The figure below illustrates the lightweight aggregate manufacturing process.
GRADATION OF AGGREGATES
Gradation is the process undergone by a material that has series of sequential degrees. One important characteristic of an aggregate is the distribution of its size particle. For example, large aggregates are beneficial in Portland cement as it requires less binder. Hence, more economical. However, it is tougher and more difficult to work into place.
Sieving Method
a sample of dry aggregates (with known weight) is filtered through a series of sieves with smaller openings. After the filtering process, the particles that were retained in each sieve will be weighted again and the obtained weight will be compared to the total initial weight of the sample before filtering. The size particles retained in each sieve size is then expressed as percent retained by weight.
Fineness Modulus
This is used to determine the degree of uniformity of the aggregate gradation.
FM = Summation(Cumulative percentage retained on specified sieves)/100
PHYSICAL PROPERTIES OF AGGREGATES
Bulk Unit Weight and Voids
Bulk Unit Weight pertains to the weight of aggregate required to fill a specific amount of volume. This is essential for the balanced mixture of Portland Cement concrete. This is determined as:
