Since wide scale coal firing for power generation began in the1920s, many millions of tons of ash and related by-products have been generated. The current annual production of coal ash world-wide is estimated around 600 million tones, with fly ash constituting about 500 million tones at 75–80% of the total ash produced.
Thus, the amount of coal waste (fly ash), released by factories and thermal power plants has been increasing throughout the world, and the disposal of the large amount of fly ash has become a serious environmental problem. The present day utilization of ash on worldwide basis varied widely from a minimum of 3% to a maximum of 57%, yet the world average only amounts to 16% of the total ash.
Fly ash is generally grey in color, abrasive, mostly alkaline, and refractory in nature. Pozzolans, which are siliceous or siliceous and aluminous materials that together with water and calcium hydroxide form cementitious products at ambient temperatures,are also admixtures.
Fly ash from pulverized coal combustion is categorized as such a pozzolan. Fly ash also contains different essential elements, including both macro nutrients P, K, Ca, Mg and micro nutrients Zn, Fe, Cu, Mn, B, and Mo for plant growth. The geotechnical properties of fly ash (e.g., specific gravity, permeability,internal angular friction, and consolidation characteristics) make it suitable for use in construction of roads and embankments, structural fill etc.
The pozzolanic properties of the ash, including its lime binding capacity makes it useful for the manufacture of cement, building materials concrete and concrete-admixed products.
Fly Ash Types :
There are two common types of fly ash: Class F and Class C.
Class F fly ash contain particles covered in a kind of melted glass. This greatly reduces the risk of expansion due to sulfate attack, which may occur in fertilized soils or near coastal areas. Class F is generally low-calcium and has a carbon content less than 5 percent but sometimes as high as 10 percent.
Class C fly ash is also resistant to expansion from chemical attack. It has a higher percentage of calcium oxide than Class F and is more commonly used for structural concrete. Class C fly ash is typically composed of high-calcium fly ashes with a carbon content of less than 2 percent.
Currently, more than 50 percent of the concrete placed in the U.S. contains fly ash.2 Dosage rates vary depending on the type of fly ash and its reactivity level. Typically, Class F fly ash is used at dosages of 15 to 25 percent by mass of cementitious material, while Class C fly ash is used at dosages of 15 to 40 percent.3
Fly Ash Applications :
Utilization of fly ash appears to be technically feasible in the cement industry. There are essentially three applications for fly ash in cement
(1) replacement of cement in Portland cement concrete
(2) pozzolanic material in the production of pozzolanic cements
(3) set retardant ingredient with cement as a replacement of gypsum
Cement is the most cost and energy intensive component of concrete. The unit cost of concrete is reduced by partial replacement of cement with fly ash.
The utilization of fly ash is partly based on economic grounds as pozzolana for partial replacement of cement, and partly because of its beneficial effects, such as, lower water demand for similar workability, reduced bleeding, and lower evolution of heat.
It has been used particularly in mass concrete applications and large volume placement to control expansion due to heat of hydration and also helps in reducing cracking at early ages.
The major drawback of fibre reinforced concrete is its low workability. To overcome this shortcoming, a material is needed, which can improve the workability without comprising strength.
The use of fly ash in concrete enhances the workability of concrete and being widely recommended as partial replacement of cement. This also reduces the cost of construction. Fly ash concrete provides much strong and stable protective cover to the steel against natural weathering action.
Stone column method for ground improvement is a vibro-replacement technique, where the weak soil is displaced using a cylindrical vibrating probe (i.e. vibroflot), thus creating a column that is then filled and compacted with good-quality stone aggregates.
With the inclusion of stone aggregates to the in situ soil, its stiffness and load-carrying capacity increases. It also helps to reduce the static as well as differential settlement of the soils.
Bulging action of the stone columns imparts lateral confinement to the surrounding soils and it also acts as a drainage path accelerating the consolidation of cohesive soils.
These stone columns are generally used for soils that are much more compressible but not weak enough to necessitate a pile foundation. Moreover, for the construction of low-to-medium rise buildings on soft soils, pile foundation sometimes becomes expensive. In such cases, stone columns are preferred.
Stone columns are very useful for the improvement of cohesive soils, marine/alluvialclays, and liquefiable soils. Stone columns have been used successfully for a widerange of applications from the construction of high-rise buildings to oil tank foundation, and for embankment and slope stabilization.
Stone column installation methods
For the installation of stone columns a vibrating poker device is used that can penetrate to the required treatment depth under the action of its own weight, vibrations, and actuated air, assisted by the pull-down winch facility of the rig.
This process displaces the soil particles and the voids created are compensated with backfilling of stone aggregates. The vibroflot penetrates the filled stone aggregates to compact it and thusforces it radially into the surrounding soils.
This process is repeated till the full depth of the stone column is completed. The lift height is generally taken as 0.6–1.2 m for the filling and compaction of the stone aggregates.
Depending upon the feeding of stone aggregates into the columns there are basically two methods for the installation of stone columns:
1- Top-feed method
In the top-feed method, the stone aggregates are fed into the top of the hole. The probe is inserted into the ground and is penetrated to the target depth under its own weight and compressed air jetting. However, jetting of water is also done especially when the soil is unstable. This also helps to increase the diameter of the stone columns and to washout the fine materials fromthe holes.
The top-feed method is suitable when water is readily available and there is enough working space to allow for water drainage. Moreover, the soil types should be such that it would not create messy surface conditions due to mud in water.
The top-feed method is preferable when a deeper groundwater level is encountered.
Stone Columns installation Top-feed Method
2- Bottom-feed method
The bottom-feed method involves the feeding of stone aggregates via a tremie pipe along the vibroflot and with the aid of pressurized air. The bottom-feed method is preferable when the soil is highly collapsible and unstable. However, the stability of holes will also depend upon the depth, boundary conditions, and the groundwater conditions. In areas, where the availability of water and space and the handling of mudin process water are limiting factors, the bottom-feed method can be implemented.
Due to limited space in the feeding system, a smaller size of aggregates is used inthe bottom-feed method compared with that used in the top-feed method. On the otherhand, the flow of stones to the column is mechanically controlled and automatically recorded in the bottom-feed method.
The purpose of the tie is to cushion and transmit the load of the train to the ballast section as well as to maintain gage.
Wood and even steel ties provide resiliency and absorption of some impact through the tie itself. Concrete ties require pads between the rail base and tie to provide a cushioning effect.
Ties are typically made of one of four materials:
Timber
Concrete
Steel
Alternative materials
1. Timber Ties
It is recommended that all timber ties be pressure-treated with preservatives to protect from insect and fungal attack. Hardwood ties are the predominate favorites for track and switch ties.
Bridge ties are often sawn from the softwood species. Hardwood ties are designated as either track or switch ties.
Factors of first importance in the design and use of ties include durability and resistance to crushing and abrasion. These depend, in turn, upon the type of wood, adequate seasoning, treatment with chemical preservatives, and protection against mechanical damage. Hardwood ties provide longer life and are less susceptible to mechanical damage.
Hardwood Track Ties
2. Concrete Ties
Concrete ties are rapidly gaining acceptance for heavy haul mainline use, (both track and turnouts), as well as for curvature greater than 2°. They can be supplied as crossties (i.e. track ties) or as switch ties. They are made of pre-stressed concrete containing reinforcing steel wires. The concrete crosstie weighs about 600 lbs. vs. the 200 lb. timber track tie.
The concrete tie utilizes a specialized pad between the base of the rail and the plate to cushion and absorb the load, as well as to better fasten the rail to the tie. Failure to use this pad will cause the impact load to be transmitted directly to
the ballast section, which may cause rail and track surface defects to develop quickly.
An insulator is installed between the edge of the rail base and the shoulder of the plate to isolate the tie (electrically). An insulator clip is also placed between the contact point of the elastic fastener used to secure the rail to the tie and the contact point on the base of the rail.
Concrete Track Ties
3. Steel Ties
Steel ties are often relegated to specialized plant locations or areas not favorable to the use of either timber or concrete, such as tunnels with limited headway clearance. They have also been utilized in heavy curvature prone to gage widening. However, they have not gained wide acceptance due to problems associated with shunting of signal current flow to ground.
Some lighter models have also experienced problems with fatigue cracking.
Steel Track Ties
4. Alternative Material Ties
Significant research has been done on a number of alternative materials used for ties. These include ties with constituent components including ground up rubber tires, glued reconstituted ties and plastic milk cartons.
Appropriate polymers are added to these materials to produce a tie meeting the required criteria. To date, there have been only test demonstrations of these materials or installations in light tonnage transit properties. It remains to be seen whether any of these materials will provide a viable alternative to the present forms of ties that have gained popularity in use.
The list of potential causes of concrete failures is a long one. A few examples include chemical reactions, shrinkage, weathering, and erosion. Many other potential causes exist, and we will explore them individually. Understanding the causes of concrete structure dam-age is an important element in the business of rehab and repair work.
1. UNINTENTIONAL LOADS
Unintentional loads are not common, which is why they are accidental. When an earth-quake occurs and affects concrete structures, that action is considered to be an accidental loading. This type of damage is generally short in duration and few and far between in occurrences.
Visual inspection will likely find spalling or cracking when accidental loadings occur. How is this type of damage stopped? Generally speaking, the damage cannot be prevented, because the causes are unexpected and difficult to anticipate. For example, an engineer is not expecting a ship to hit a piling for a bridge, but it happens. The only defense is to build with as much caution and anticipation as possible.
2. CHEMICAL REACTIONS
Concrete damage can occur when chemical reactions are present. It is surprising how little it takes for a chemical attack on concrete to do serious structural damage.
Examples of chemical reactions and how they affect concrete:
a- Acidic Reactions
Most people know that acid can have serious reactions with a number of materials, and concrete is no exception. When acid attacks concrete, it concentrates on its products of hydration. For example, calcium silicate hydrate can be adversely affected by exposure to acid.
Sulfuric acid works to weaken concrete and if it is able to reach the steel reinforcing members, the steel can be compromised. All of this contributes to a failing concrete structure.
Visual inspections may reveal a loss of cement paste and aggregate from the matrix. Cracking, spalling, and discoloration can be expected when acid deteriorates steel reinforcements, and laboratory analysis may be needed to identify the type of chemical causing the damage.
b- Aggressive Water
Aggressive water is water with a low concentration of dissolved minerals. Soft water is considered aggressive water and it will leach calcium from cement paste or aggregates. This is not common in the United States. When this type of attack occurs, however, it is a slow process. The danger is greater in flowing waters, because a fresh supply of aggressive water continually comes into contact with the concrete.
If you conduct a visual inspection and find rough concrete where the paste has been leached away, it could be an aggressive-water defect. Water can be tested to determine if water quality is such that it may be responsible for damage. When testing indicates that water may create problems prior to construction, a non-Portland-cement-based coating can be applied to the exposed concrete structures.
c- Alkali-Carbonate Rock Reaction
Alkali-carbonate rock reaction can result in damage to concrete, but it can also be beneficial. Our focus is on the destructive side of this action, which occurs when impure dolomitic aggregates exist. When this type of damage occurs, there is usually map or pattern cracking and the concrete can appear to be swelling.
Alkali-carbonate rock reaction differs from alkali-silica reaction because there is a lack of silica gel exudations at cracks. Petrographic examination can be used to confirm the presence of alkali-carbonate rock reaction. To prevent this type of problem, contractors should avoid using aggregates that are, or are suspected to be, reactive.
d- Alkali-Silica Reaction
An alkali-silica reaction can occur when aggregates containing silica that is soluble in highly alkaline solutions may react to form a solid, non expansive, calcium-alkali-silica complex or an alkali-silica complex that can absorb considerable amounts of water and expand. This can be disruptive to concrete.
Alkali-silica reaction in concrete
Concrete that shows map or pattern cracking and a general appearance of swelling could be a result of an alkali-silica reaction. This can be avoided by using concrete that contains less than 0.60% alkali.
e- Various Chemical Attacks
Concrete is fairly resistant to chemical attack. For a substantial chemical attack to have degrading effects of a measurable nature, a high concentration of chemical is required. Solid dry chemicals are rarely a risk to concrete. Chemicals that are circulated in contact with concrete do the most damage.
When concrete is subjected to aggressive solutions under positive differential pressure, the concrete is particularly vulnerable. The pressure can force aggressive solutions into the matrix. Any concentration of salt can create problems for concrete structures. Temperature plays a role in concrete destruction with some chemical attacks. Dense concrete that has a low water–cement ratio provides the greatest resistance.
The application of an approved coating is another potential option for avoiding various chemical attacks.
f- Sulfate Situations
A sulfate attack on concrete can occur from naturally occurring sulfates of sodium, potassium, calcium, or magnesium. These elements can be found in soil or in ground water. Sulfate ions in solution will attack concrete. Free calcium hydroxide reacts with sulfate to form calcium sulfate, also known as gypsum. When gypsum combines with hydrated calcium aluminate it forms calcium sulfoaluminate.
Either reaction can result in an increase in volume. Additionally, a purely physical phenomenon occurs where a growth of crystals of sulfate salts disrupts the concrete. Map and pattern cracking are signs of a sulfate attack. General disintegration of concrete is also a signal of the occurrence.Sulfate attacks can be prevented with the use of a dense, high-quality concrete that has a low water–cement ratio. A Type V or Type II cement is a good choice.
If pozzolan is used, a laboratory evaluation should be done to establish the expected improvement in performance.
g- Poor Workmanship
Poor workmanship accounts for a number of concrete issues. It is simple enough to follow proper procedures, but there are always times when good practices are not employed. The solution to poor workmanship is to prevent it. This is much easier said than done. All sorts of problems can occur when quality workmanship is not assured and some of the key causes for these problems are as noted below:
Adding too much water to concrete mixtures
Poor alignment of formwork
Improper consolidation
Improper curing
Improper location and installation of reinforcing steel members
Movement of formwork
Premature removal of shores or reshores
Settling of concrete
Settling of subgrade
Vibration of freshly placed concrete
Adding water to the surface of fresh concrete
Miscalculating the timing for finishing concrete
Adding a layer of concrete to an existing surface
Use of a tamper
Jointing
3. CORROSION
Corrosion of steel reinforcing members is a common cause of damage to concrete. Rust staining will often be present during a visual inspection if corrosion is at work. Cracks in concrete can tell a story. If they are running in straight lines, as parallel lines at uniform intervals that correspond with the spacing of steel reinforcement materials, corrosion is prob-ably at the root of the problem. In time, spalling will occur. Eventually, the reinforcing mate-rial will become exposed to a visual inspection.
Techniques for stopping, or controlling, corrosion include the use of concrete with low permeability. In addition, good workmanship is needed. Some tips to follow include:
Use as low a concrete slump as
Cure the concrete
Provide adequate concrete cover over reinforcing
Provide suitable
Limit chlorides in the concrete
Pay special attention to any protrusions, such as bolts and
4.FREEZING AND THAWING
Freezing and thawing during the curing of concrete is a serious concern. Each time the concrete freezes, it expands. Hydraulic structures are especially vulnerable to this type of damage. Fluctuating water levels and under-spraying conditions increase the risk. Using deicing chemicals can accelerate damage to concrete with resultant pitting and scaling. Core samples will probably be needed to assess damage.
Prevention is the best cure. Provide adequate drainage, where possible, and work with low water–cement ratio concrete. Use adequate entrained air to provide suitable air-void systems in the concrete. Select aggregates best suited for the application, and make sure that concrete cures properly.
5. SETTLEMENT AND MOVEMENT
Settlement and movement can be the result of differential movement or subsidence. Concrete is rigid and cannot stand much differential movement. When it occurs, stress cracks and spall are likely to occur. Subsidence causes entire structures or single elements of entire structures to move. If subsidence is occurring, the concern is not cracking or spalling; the big risk is stability against overturning or sliding.
A failure via subsidence is generally related to a faulty foundation. Long-term consolidations, new loading conditions, and related faults are contributors to subsidence. Geotechnical investigations are often needed when subsidence is evident.
Cracking, spalling, misaligned members, and water leakage are all evidence of structure movement. Specialists are normally needed for these types of investigations.
6. SHRINKAGE
Shrinkage is caused when concrete has a deficient moisture content. It can occur while the concrete is setting or after it is set. When this condition happens during setting, it is called plastic shrinkage; drying shrinkage happens after concrete has set.
Plastic shrinkage is associated with bleeding, which is the appearance of moisture on the surface of concrete. This is usually caused by the settling of heavier components in a mixture. Bleed water typically evaporates slowly from the surface of concrete.
Concrete Shrinkage
When evaporation occurs faster than water is supplied to the surface by bleeding, high-tensile stresses can develop. This stress can lead to cracks on the concrete surface.Cracks caused by plastic shrinkage usually occur within a few hours of concrete placement.
These cracks are normally isolated and tend to be wide and shallow. Pattern cracks are not generally caused by plastic shrinkage.
Weather conditions contribute to plastic shrinkage. If the conditions are expected to be conducive to plastic shrinkage, protect the pour site with windbreaks, tarps, and similar arrangements to prevent excessive evaporation. In the event that early cracks are discovered, revibration and refinishing can solve the immediate problem. Drying shrinkage is a long-term change in volume of concrete caused by the loss of moisture.
A combination of this shrinkage and restraints will cause tensile stresses and lead to cracking. The cracks will be fine and the absence of any indication of movement will exist. The cracks are typically shallow and only a few inches apart. Look for a blocky pattern to the cracks.
They can be confused with thermally induced deep cracking, which occurs when dimensional change is restrained in newly placed concrete by rigid foundations or by old lifts of concrete.
To reduce drying shrinkage, try the following precautions:
Use less water in
Use larger aggregate to minimize paste
Use a low temperature to cure concrete
Dampen the subgrade and the concrete
Dampen aggregate if it is dry and
Provide adequate
Provide adequate contraction joints
7. FLUCTUATIONS IN TEMPERATURE
Fluctuations in temperature can affect shrinkage. The heat of hydration of cement in large placements can present problems. Climatic conditions involving heat also affect concrete; for example, fire damage, while rare, can also contribute to problems associated with excessive heat.
There are several types of TBMs. The best TBM for a project is based on the geological conditions of the site and the project’s features.The general classification of the different types of TBMs for both hardrock and soft ground are presented here.
Fig 1. TBM’s Classification
1. Gripper Tunnel Boring Machine
A gripper TBM is a rock tunnel boring machine which generally utilizes roller disc cutters as excavation tools and which moves forward by reacting (i.e., exerting shove forces) against the tunnel walls through a hydraulic gripper reaction system.
It is is suitable for driving in hard rock conditionswhen there is no need for a final lining. The rock supports (rock anchors, wire-mesh, shotcrete, and/or steel arches) can be installed directly behindthe cutter head shield and enable controlled relief of stress and deformations.
The existence of mobile partial shields enables gripper TBMs to be flexible even in high-pressure rock. This is useful when excavating in expanding rock to prevent the machine from jamming.
Fig 2. Typical diagram of an open gripper main beam TBM.Courtesy of TheRobbins Company
2. Double-Shield Tunnel Boring Machine
A double-shield TBM is generally considered to be the fastest machine for hard rock tunnels under favorable geological conditions with installation of the segment lining. It is possible to drive 100 m in 1 day. This type of TBM consists of a rotating cutter head and double shields (Fig. 3), a telescopic shield (an inner shield that slides within the large router shield), and a gripper shield together with a shield tail.
While boring, gripper shoes radially press against the surrounding rock to hold the machine in place and take some of the load from the thrust cylinders. For the motion of the front shield the gripper shoes are loosened, before the front shield is pushed forward by thrust cylinders protected by the extension of the telescopic shield.
Because regripping is a fast process, double-shield TBMs can almost continuously drill. As for the shield tail, it is used to provide protection for workers while erecting,installing the segment lining, and pea grouting.
Fig 3. Typical diagram of a double-shield TBM.Courtesy of The Robbins Company
3. Single-Shield Tunnel Boring Machine
Single-shield TBMs (Fig. 4) are used in soils that do not bear ground-water and where rock conditions are less favorable than for double shields, such as in weak fault zones. The shield is usually short so that a small radius of curvature can be achieved.
Fig 4. Typical diagram of single-shield TBM.Courtesy of The Robbins Company
4. Earth Pressure Balance Machines
Earth pressure balance (EPB) technology (Fig. 5) is suitable for digging tunnels in unstable ground such as clay, silt, sand, or gravel. An earth paste face formed by the excavated soil and other additives supports the tunnel face. Injections containing additives improve the soil consistency, reduce soil stick, and thus its workability.To ensure support pressure transmission to the soil, the earth paste is pressurized through the thrust force transfer into the bulkhead.
The TBM advance rate (in flow of excavated soil) and the soil outflow from the screw conveyor regulate the support pressure at the tunnel face. This is monitored at the bulkhead by the readings of pressure sensors.
Fig 5. Scheme of an EPB machine
5. Slurry Tunnel Boring Machine
Slurry TBMs are used for highly unstable and sandy soil and when the tunnel passes beneath structures that are sensitive to ground disturbances. Pressurized slurry (mostly bentonite) supports the tunnel face. The support pressure is regulated by the suspension inflow and outflow. The slurry’s rheology must be chosen in accordance with the soil parameters and should be carefully and regu-larly monitored.
6. Mixshield Technology
Mixshield technology (Fig. 6) is a variant of conventional slurry technology for heterogeneous geologies and high water pressure. In mixshield technology an automatically controlled air cushion controls the support pressure, with a submerged wall that divides the excavation chamber.This wall seals off the machine against the excess pressure from the tunnel’s face. As air is compressible in nature, the mixshield is more sensitive in pressure control and thus will provide more accurate control of ground settlement.
Fig 6. Overview of a mixshield TBM.Courtesy of Herrenknecht AG
7. Pipe Jacking
Pipe jacking (also called microtunneling) is a micro- to small-scale tunneling method for installing underground pipelines with minimum surface disruption. It is used for sewage and drainage construction, sewer replace-ment and lining, gas and water mains, oil pipelines, electricity and telecommunications cables, and culverts .
A fully automated mechanized tunneling shield is usually jacked forward from a launch shaft toward a reception shaft. Jacking pipes are then progressively inserted into the working shaft. Another significant difference between the pipe jacking method and shield method is that the lining of the pipe jacking is made of tubes and the lining of the shield method is made up of segments. In order to significantly reduce the resistance of the pipes, a thixotro-pic slurry is injected into the outside perimeter of the pipes. The thixo-tropic slurries can also reduce disturbance to the ground while pipe jacking slurry thickness. The thickness should be six to seven times thevoid between the machine and pipes.
Fig 7. Typical Components of a Pipe Jacking Operation
8. Partial-Face Excavation Machine
Partial-face excavation machines (Fig. 8) have an open-face shield andcan sometimes be more economical in homogeneous and semistable ground with little or no groundwater. In boulders layer, the open-face can deal with boulders much easier than closed shield machines. In cavity ground, the open-face can avoid the risk of falling down into the bottom of the cavity. Thanks to their simple design and that the operator workplace is close to the open tunnel face,these machines can easily be adapted to changing geological conditions. Good excavation monitoring can also be carried out.
Fig 8. Two kinds of partial-face excavation machines.Courtesy ofHerrenknecht AG
Soil Nail – Helping Combat Climate Change with Extraordinary Geotechnical Techniques
Pollution caused global warming which threatens our climate, our Earth. There have been significant changes in the behavior of Earth’s top layer and climate.
The risks of climate change require swift and deep reductions in emissions of heat-trapping gases and investments to prepare for now unavoidable impacts. Geo engineering is just one measure to combat the daunting challenge of keeping the rise in global temperatures in check.
Geo engineering or Climate engineering is the intentional large-scale intervention in the Earth’s climate system to counter climate change. It includes techniques like removing CO2 from the atmosphere, and steps to rapidly cool the Earth by reflecting solar energy back to space.
Geotechnical Engineering is a part of geoengineering that involves the application of soil and rock mechanics as well as engineering geology to solve engineering problems. These are design of foundations, slopes, excavations, dams, tunnels and other Civil, Mining and Environmental engineering projects relating to the mechanical response of the ground, and the water within it. It deals with many types of infrastructure – tunnels, bridges, dams, buildings, roads, railways, ports and landfills – that are built on the ground.
Soil nailing and its advantages
Soil nailing implies using grouted, tension-resisting steel elements (nails) to reinforce in situ soils and creating a gravity retaining wall for permanent or temporary excavation support.
Common uses
Stabilize slopes and landslides
Support excavations
Repair existing retaining walls
Advantages
Equipment is small enough to use in areas with restricted access
Often a more cost effective and faster solution for excavation support
Can be installed from crane-suspended working platforms for existing steep slopes, such as bluffs or existing retaining walls
Allows excavation to start at the same time as the shoring system is being installed
What are the main types Of Grout Used In Construction
What Is Grout?
Grout is a thick paste that is used to fill gaps, voids, or joints. It is mainly a composite material used for grouting, repairing concrete cracks, filling gaps and sealing the joints between tiles, waterproofing, soil stabilization, etc.
In this article, I will discuss different types of grout materials used in construction, tile installation, and other works. Differing from mortar, grout has a low viscosity and lack of lime, which makes it thinner and easier to work with.
Types Of Grout:
1. Cementitious Grout:
Cementitious grouts are the traditional grouting material, used both in residential as well as some commercial applications. It is also known as slurry grouting or hydraulic cement grouting. Materials used in cementitious grout are :
Portland cement,
Filler particles of different sizes,
Water-retentive additive,
Colored pigments.
Cementitious grouts are available in a variety of colors that let you match or contrast with the tile. Water is mixed with the grout and then applied using a trowel. The water retentive ingredient in cementitious grouts slows down the drying time, allowing the cement to cure slowly achieving maximum hardness.
Cementitious grouts are further classified into three types:
Sanded grout
Unsanded /Non-sanded grout
Latex modified grout.
a. Sanded Grout:
Sanded grout is composed of portland cement, sand, and other additives. The sand used is relatively larger in size. It is typically recommended for tile floors where joints are 1/8 inch to 3/8 inch wide. Sand provides extra strength to the grout joints, as it is one of the best building materials.
Sanded grout is absorbent and easily attracts dirt, therefore it is always better to seal the joint when grouting is done. As sand easily makes scratches, this type of grout should not be used on easily scratched tile like marble.
Sanded tile grout is less costly than unsanded grout because sand is a cheaper filler than polymers. It also provides a tight lock and a neat & clean finish.
Sanded grouts are ideal for use in Kitchen floor Bathroom floor Entryways Shower pan etc.
b. Unsanded Grout:
Unsanded grout is made of portland cement and color powder pigments. No sand is used here hence also known as non-sanded grout.
This type of grout is suitable for joint thickness between 1/8 to 1/16 inches. Unlike sanded grout, it is useful in scratchable surfaces such as metal, glass, marble, and natural stone tile.
Unsanded grout provides a much smoother texture since the mineral particles present in it are very fine powders without having grit. However, these grouts easily develop cracks due to lack of binding power.
Unsanded grout is costly than sanded and you may have limited color options. Unsanded grouts are suitable for use in Rectified tiles, Polished stones. Bathroom walls, Shower walls etc.
c. Latex Modified Grout:
Sanded grouts may be composed of a latex polymer additive which increases the strength and water-proofing properties of grout. The additives can be mixed in both dry and wet conditions.
2. Chemical Grouts:
Chemical grouts consist of polymers such as epoxy, acrylic, polyurethane, sodium silicate, or any other suitable polymer. It requires injection of chemical grouts into finer cracks that are not groutable by cementitious grouts. Some useful types of chemical grouts are discussed below.
a. Epoxy Grout:
Epoxy grout is consists of epoxy resin, silica fillers, pigments, and a hardener. It neither uses Portland cement nor uses water during the mixing process.
Epoxy grout is very strong and durable. Additionally, it is highly resistant to stains, cracks, chemicals attack, harsh weather conditions, and climatic changes.
Epoxy grouts are considerably less porous than cementitious grouts and set up quickly. It is also much costlier than any other type of grout. With light maintenance, epoxy grout can last lifelong if applied correctly.
The strength and other properties make it perfect for any tile work, indoors or outdoors. It is suitable for use in High traffic areas like entryways, hallways, and foyers.
Any type of flooring exposed to harsh conditions like grease and acid. Kitchen counters and backsplash, bathrooms, etc. Keep in mind, porous and unglazed surfaces, such as limestone or quarry tiles need to be sealed before applying epoxy grout, otherwise, it can stain the tile surfaces badly.
Another major disadvantage that it is much more difficult to shape and slope. If not done correctly, it will look plastic.
b. Furan Grout:
Furan grout is similar to epoxy but composed of polymers of fortified alcohols. There is no water used in this type of grout installation. Furan is basically a combination of furan resin and a filler powder with an acid catalyst.
The acid catalyst helps the resin to cure making it a thermosetting resin that has unsurpassed chemical, physical, and thermal resistance.
The tile surfaces may be smooth, abrasive or non-skid hence it should be sealed with wax coating right after furan grout installation to protect from staining. Furan grout is the strongest and most expensive grout material available in the market.
Because of the difficulty of installation, it requires proper precautions and skilled labours. This type of grout is suitable for use in Brick pavers, Quarry tiles. Industrial projects, such as laboratories, factories, dairies, and meat-packing plants. Areas highly exposed to chemicals and/or grease.
c. Acrylic Grout:
Acrylic grout is an acrylic latex admixture composed for use as a substitute for water when grouting ceramic tile. It is specifically produced for use with AccuColor Portland cement grouts. Acrylic grout helps to make joints less susceptible to water penetration.
It is very much essential when grouting wet areas. The additive further helps the grout retaining its color and resisting stains. It gives good stability in freezes and thaws. It also enhances grout flexibility. It has greater adhesion properties. Additionally, you don’t need to cover the entire work surface.
You can just apply it in between tile joints. Another advantage of using acrylic latex grout is that it can be used in small spaces. It is mostly suitable for joint thickness less than 1/8 inch. This type of grout is especially suitable for use in Outdoors such as deck or garage projects. Fast-food restaurant floors. Marble work etc.
A culvert is a covered channel of relatively short length designed to pass water through an embankment (e.g. highway, railroad and dam).
It is a hydraulic structure and it may carry flood waters, drainage flows, natural streams below earthfill and rockfill structures. From a hydraulic aspect, a dominant feature of a culvert is whether it runs full or not.
The design can vary from a simple geometry (i.e. box culvert) to a hydraulically smooth shape (i.e. minimum energy loss (MEL) culvert)
Culvert Parts :
A culvert consists of three parts: the intake (also called inlet or fan), the barrel (or throat) and the diffuser (also called outlet or expansion fan) (Fig.1-a).
The cross-sectional shape of the barrel may be circular (i.e. pipe), rectangular (i.e box culvert) or multi-cell (e.g. multi-cell box culvert) (Fig.1-b).
The bottom of the barrel is called the invert while the barrel roof is called the soffit or obvert. The training walls of the inlet and outlet are called wing walls.
Fig 1. Sketch of a culvert: (a) box culvert
Fig 1. (b) MEL culvert
Standard Culverts :
A standard culvert is designed to pass waters at a minimum cost without much consideration of the head loss. The culvert construction must be simple: e.g. circular pipes and precast concrete boxes.
MEL Culverts :
An MEL culvert is a structure designed with the concept of minimum head loss. The flow in the approach channel is contracted through a streamlined inlet into the barrel where the channel width is minimum, and then it is expanded in a streamlined outlet before being finally released into the downstream natural channel. Both the inlet and outlet must be streamlined to avoid significant form losses
Rivets are non threaded fasteners that are usually manufactured from steel or aluminium. They consist of a preformed head and shank, which is inserted into the material tobe joined and the second head that enables the rivet to function as a fastener is formedon the free end by a variety of means known as setting.
A conventional rivet before and after setting is illustrated in Fig. 1.
Fig.1 Conventional rivet before and after setting
Rivets are widely used to join components in aircraft (e.g. see Fig.2) boilers, ships and boxes and other enclosures. Rivets tend to be much cheaper to install than bolts and the process can be readily automated with single riveting machines capable of installing thousands of rivets an hour.
Fig 2. Two historical examples of the use of rivets on the Lockheed Electra and RB211engine nacelle.
Rivets can be made from any ductile material such as carbon steel, aluminium and brass. A variety of coatings are available to improve corrosion resistance. Care needs to be taken in the selection of material and coating to avoid the possibility of corrosion by galvanic action.
In general a given size rivet will be not as strong as the equivalent threaded fastener.
The two main types of rivet are tubular and blind and each type are available in amultitude of varieties. The advantage of blind rivets (Fig.3) is that they require access to only one side of the joint.
Fig 3. An example of the application of a closed end blind rivet
A further type of rivet with potentially many over-all advantages, from the production perspective, is the self-piercing rivet that does not require a predrilled hole. The rivet is driven into the target materials with high force, piercing the top sheets and spreading outwards into the bottom sheet of material under the influence of an upsetting die to form the joint.
Factors in the design and specification of rivets include the size, type and material for the rivet, the type of joint, and the spacing between rivets.
There are two main types of riveted joint: lap-joints and butt-joints(Fig.4).
In lap joints the components to be joined overlap each other, while for butt joints an additional piece of material is used to bridge the two components to be joined which are butted up against each other.
Rivets can fail by shearing through one cross-section known as single shear, shearing through two cross-sections known as double shear, and crushing. Riveted plates can fail by shearing, tearing and crushing.
IFC or Industry Foundation Classes is a global standard for describing, sharing and exchanging information on building and facility management.
To encourage interoperability between BIM applications from several companies it was created the IFC format, specified and developed by buildingSMART.
The IFC format is a repository of data for open building semantic information object, including geometry, properties and relationships to facilitate :
the interdisciplinary coordination during the construction of the information models, including design disciplines as architecture, structural or services, as well as during the construction phase;
the data sharing and exchange between IFC applications;
the transference and reuse of data for analysis and other further tasks.
The IFC initiative began in 1994 when Autodesk started to develop a set of C ++ classes that could support the development of integrated applications. Twelve other American companies have joined the initiative, initially defined as the Alliance for Interoperability.
In 1997, the name was changed to International Alliance for Interoperability due to the integration of more international companies. This new alliance was reconstituted as a non-profit organization with the goal of developing the IFC as a neutral product for the architectural, engineering and construction industry.
The designation of this initiative was again changed to buildingSMART in 2005.
In 1997 it was launched the first version of the IFC format. Over the years, the IFC format has been improved and new versions have been released.
The improvements are based not only on the optimization of the various features previously supported by the format, but also in increasing the variety of information supported.
As an example, just after the IFC 2×2 version it was possible to transfer structural designs, once BIM modules applications dedicated to the structure design have arisen later. However, only in the latest release, IFC 2×4, it became possible, for example, transfer via IFC modeled reinforcement on construction elements, such as walls or slabs.
The IFC schema is constantly evolving. The current version, released in 2013, is IFC 4 (the prior releases were labelled as 1.0, 1.5, 1.51 and then 2x, 2×2, 2×3).
