Shotcrete mix design and proportion

Aggregate

Aggregates for shotcrete my contain river sand, crushed sand and crushed stone with particle sizes up to 16mm, normally up to 9.5mm.

Here after is a typical and recommended gradation of combined aggregates for shotcrete that will resulted in perfect mix design.:

Water Cement Ratio

The water-cement ratio for wet shotcrete normally falls within a range of by weight and 0.40 to 0.55 for wet-mix shotcrete.

Dry mix design shall only include water content enough for the hydration process of cement needed for strength development.

In dry-mix shotcrete, the moisture content of the fine and coarse aggregates should be such that the aggregate-cement mixture will flow at a uniform rate, without slugging or hose plugging. The optimum moisture content is generally within the range of 3 to 6 percent. The sand should be dried or wetted as required to bring the moisture content within that range. Large fluctuations in moisture content should be avoided.

A crude but effective test for determining proper predampening is the “ball-in-hand” test. A small amount of mix is placed in the hand and squeezed tightly. When the hand is opened, the mixture may crumble into discrete particles which indicates too little predampening moisture and is usually light gray. If the material holds together, or cracks but remains essentially whole, there is enough moisture. If moisture comes off on the hand, there is too much moisture in the mix.

Unit Weight of Concrete

The unit weight of good shotcrete is usually between 2230 to 2390 kg/m3, about the same as conventional concrete.

Cement Content

OPC cement with surface Blaine above 4500 cm2/gr is most suitable for shotcrete. Typical and recommended cement contents is:

* It is in the best interest of the end user to perform trial mixes and shotcrete trial to determine the suitable cement content, to meet other parameters, above table is used only as a guide in preliminary design and shall be decided in the results of trial mixes and trial application.

Proportioning

Shotcrete design for wet process can be designed like conventional concrete but these mixes contains higher volume of fine aggregate and cement. Shotcrete process can be designed by absolute volume method or by weight.

Shotcrete design for dry process is designed using the bulk densities of the materials, usually the water content is not included in the calculation.

Construction Specifications

Specifications of work quality are an important feature of facility designs. Specifications of required quality and components represent part of the necessary documentation to describe a facility. Typically, this documentation includes any special provisions of the facility design as well as references to generally accepted specifications to be used during construction.

General specifications of work quality are available in numerous fields and are issued in publications of organizations such as the American Society for Testing and Materials (ASTM), the American National Standards Institute (ANSI), or the Construction Specifications Institute (CSI). Distinct specifications are formalized for particular types of construction activities, such as welding standards issued by the American Welding Society, or for particular facility types, such as the Standard Specifications for Highway Bridges issued by the American Association of State Highway and Transportation Officials. These general specifications must be modified to reflect local conditions, policies, available materials, local regulations and other special circumstances.

Construction specifications normally consist of a series of instructions or prohibitions for specific operations. For example, the following passage illustrates a typical specification, in this case for excavation for structures:

Conform to elevations and dimensions shown on plan within a tolerance of plus or minus 0.10 foot, and extending a sufficient distance from footings and foundations to permit placing and removal of concrete formwork, installation of services, other construction, and for inspection. In excavating for footings and foundations, take care not to disturb bottom of excavation. Excavate by hand to final grade just before concrete reinforcement is placed. Trim bottoms to required lines and grades to leave solid base to receive concrete.

This set of specifications requires judgment in application since some items are not precisely specified. For example, excavation must extend a “sufficient” distance to permit inspection and other activities. Obviously, the term “sufficient” in this case may be subject to varying interpretations. In contrast, a specification that tolerances are within plus or minus a tenth of a foot is subject to direct measurement. However, specific requirements of the facility or characteristics of the site may make the standard tolerance of a tenth of a foot inappropriate. Writing specifications typically requires a trade-off between assuming reasonable behavior on the part of all the parties concerned in interpreting words such as “sufficient” versus the effort and possible inaccuracy in pre-specifying all operations.

In recent years, performance specifications have been developed for many construction operations. Rather than specifying the required construction process, these specifications refer to the required performance or quality of the finished facility. The exact method by which this performance is obtained is left to the construction contractor. For example, traditional specifications for asphalt pavement specified the composition of the asphalt material, the asphalt temperature during paving, and compacting procedures. In contrast, a performance specification for asphalt would detail the desired performance of the pavement with respect to impermeability, strength, etc. How the desired performance level was attained would be up to the paving contractor. In some cases, the payment for asphalt paving might increase with better quality of asphalt beyond some minimum level of performance.

Some properties of concrete using microsilica

What is microsilica or silica fume?

Microsilica (silica fume) results from the reduction of quartz (SiO2) by carbon in the electric arc furnace. Part of the only partially reduced quartz evaporates as SiO and is re-oxidized to SiO2, when it comes in contact with oxygen in a cooler part of the furnace. This SiO2 condenses in tiny microscopic spherical particles as amorphous silicon dioxide with average grain size of 0.1 micron. Microsilica particles are thus about 100 times finer than a grain of cement.

Properties of concrete using microsilica or silica fume?

1. Highest strength

By the reaction cement-superplasticizer-microsilica, strengths hitherto never achieved are possible.
Extremely strong concrete using microsilica ca almost reach the strength of steel.

2. Weight saving

Possibility for tall building have been improved, not only because of the high strength of microsilica concrete but also because of weight saving.

3. Permeability to water
An additional of 10% microsilica and superplasticizer reduces the permeability to one tenth.

4. Resistance to frost and road salt
Microsilica improves the chemical resistance to sulphates, chlorides, (road salt), alkali-reative aggregates, acids, carbon dioxide (carbonation), sulphur dioxide and nitrous gases. Resistance to freeze-thaw with road salts are greatly improved.

5. Corrosion resistance
For steel to rust, for important conditions must be fulfilled. There must be: an electrolytic cell in which there is an anode where ions go into solution and electrons are released; an electrical conductor, in this case the reinforcing steel, which transports the electrons from the anode to cathode; the cathode where the electrons are used up in the presence of acid and dampness; and an electrolyte, the dampness of the concrete which allows ions to move between cathode and anode. It is the reactions at the cathode which control the speed of rusting. Thus when neither acid nor water can diffuse to the steel, rusting cannot occur. By reduction of the permeability and of the electrical conductivity through the combination of calcium hydroxide, microsilica improves the rust resistance of steel in concrete.

6. Chloride penetration and carbonation
The high alkalinity of cement protects the reinforcing steel naturally against rust. The pH value if cement paste is about 12.5 and thus passiveness the steel so that even in the presence of acid and damp it cannot rust. The action of carbon dioxide from the air reduces the alkalinity continuously by neutralizing the lime. If the carbonated region reaches the steel it begins to rust. With chlorides, whether from road salt or seawater, rusting begin at high PH value and even at a high rate. The consequence are known. But if carbonation is stopped and the entry of chlorides is made difficult, the reinforcement corrosion can be prevented.

7. Bond with reinforcement
With increasing microsilica content the bond strength between concrete and steel improves.

8. Abrasion resistance
High abrasion resistance is needed for many applications. The property can be greatly improve by the use of microsilica.

9. Temperature resistance
Combination of the free substances, cement, microsilica and superplasticizer can produce materials of very high strength. Surprisingly, the compressive strength is maintained even above 400 Celsius degrees.

Construction Surveying

Construction surveying is generally performed by specialised technicians. Unlike land surveyors, the resulting plan does not have legal status. Construction surveyors perform the following tasks:

• Survey existing conditions of the future work site, including topography, existing buildings and infrastructure, and even including underground infrastructure whenever possible (for example, measuring invert elevations and diameters of sewers at manholes);
• Construction surveying (otherwise “lay-out” or “setting-out”): to stake out reference points and markers that will guide the construction of new structures such as roads or buildings for subsequent construction. These markers are usually staked out according to the arbitrary coordinate system used for the project;
• Verify the location of structures during construction;
• As-Built surveying: a survey conducted at the end of the construction project to verify that the work authorized was completed to the specifications set on plans.

“Coordinate Systems used in Construction”

Land surveys and surveys of existing conditions are generally performed according to [geodesic] coordinates. However for the purposes of construction an arbitrary construction coordinate system will often be used. During construction surveying, the surveyor will often have to convert from geodesic coordinates to the arbitrary coordinate system used for that project.

In the case of roads or other linear [infrastructure], a “chainage” will be established, often to correspond with the center line of the road. During construction, structures would then be located in terms of “chainage”, “offset” and “elevation”. “Offset” is said to be “left” or “right” relative to someone standing on the “chainage line” who is looking in the direction of increasing “chainage”. Plans would often show “plan” views (viewed from above), “profile” views (a “transparent” section view collapsing all section views of the road parallel to the “chainage”) or “cross-section” views (a “true” section view perpendicular to the “chainage”). In a “plan” view, “chainage” generally increases from left to right, or from the bottom to the top of the plan. “Profiles” are shown with the chainage increasing from left to right, and “cross-sections” are shown as if the viewer is looking in the direction of increasing chainage (so that the “left” “offset” is to the “left” and the “right” “offset” is to the “right”).

“Building Axes”

In the case of buildings, an arbitrary system of axes is often established so as to correspond to the rows of columns and the major load-bearing walls of the building. The axes may be identified alphabetically in one direction, and numerically in the other direction (as in a road map). The axes are usually but not necessarily perpendicular, and are often but not necessarily evenly spaced. Floors and basement levels are also numbered. Structures, equipment or architectural details may be located in reference to the floor and the nearest intersection of the arbitrary axes.

“Reference Lines”

In other types of construction projects, arbitrary “north-south” and “east-west” reference lines may be established, that do not necessarily correspond to true coordinates.

Concrete admixtures

Concrete materials and concrete applications have changed and improved in the last 100 years.  Whilst concrete admixtures have been around for many years, there has been an extensive amount of development of new admixtures in recent years. It is probable that almost all concrete used around the world today contains some types of admixtures.  Admixtures added to the concrete can modify its properties on both the fresh and hardened stages, but are used primarily to modify the properties of fresh or plastic concrete.

Admixture s can be employed to entrain air for free-thaw resistance, to accelerate or retard setting time, to control  strength development, to achieve shrinkage compensation and to improve workability. Most of unwanted effects of early admixtures have been overcome (such as the retarding effect of early plasticizers) so that modern admixture do not pacl “unexpected surprises”.

The most dramatic development have been in the area of superplasticizers or high range water reducers. These products now allow high level of water reduction without a loss in workability. Whilst early superplasticizers had a limited time over which they were effective, modern superplasticisers allow sufficient control for the setting in, for example, a large pour, until all the concrete has been placed.

Care should be taken when designing concrete mixes containing admixtures to assess sensitivity to changes of properties with changes in other ingredients and mix designs should be done on the specific materials that will be used.

Civil Engineering & Sub Diciplines

Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings. Civil engineering is the oldest engineering discipline after military engineering, and it was defined to distinguish non-military engineering from military engineering It is traditionally broken into several sub-disciplines including environmental engineering, geotechnical engineering, structural engineering, transportation engineering, municipal or urban engineering, water resources engineering, materials engineering, coastal engineering  surveying, and construction engineering Civil engineering takes place on all levels: in the public sector from municipal through to national governments, and in the private sector from individual homeowners through to international companies.

 

Sub-disciplines

In general, civil engineering is concerned with the overall interface of human created fixed projects with the greater world. General civil engineers work closely with surveyors and specialized civil engineers to fit and serve fixed projects within their given site, community and terrain by designing grading, drainage, pavement, water supply, sewer service, electric and communications supply, and land divisions. General engineers spend much of their time visiting project sites, developing community consensus, and preparing construction plans. General civil engineering is also referred to as site engineering, a branch of civil engineering that primarily focuses on converting a tract of land from one usage to another. Civil engineers typically apply the principles of geotechnical engineering, structural engineering, environmental engineering, transportation engineering and construction engineering to residential, commercial, industrial and public works projects of all sizes and levels of construction.

 Coastal engineering

Coastal engineering is concerned with managing coastal areas. In some jurisdictions the terms sea defense and coastal protection are used to mean, respectively, defence against flooding and erosion. The term coastal defence is the more traditional term, but coastal management has become more popular as the field has expanded to include techniques that allow erosion to claim land.

Construction engineering

Construction engineering involves planning and execution of the designs from transportation, site development, hydraulic, environmental, and structural and geotechnical engineers. As construction firms tend to have higher business risk than other types of civil engineering firms, many construction engineers tend to take on a role that is more business-like in nature: drafting and reviewing contracts, evaluating logistical operations, and closely monitoring prices of necessary supplies.

Earthquake engineering

Earthquake engineering covers ability of various structures to withstand hazardous earthquake exposures at the sites of their particular location.
Earthquake engineering is a sub discipline of the broader category of Structural engineering. The main objectives of earthquake engineering are

• Understand interaction of structures with the shaky ground.

• Foresee the consequences of possible earthquakes.

• Design, construct and maintain structures to perform at earthquake exposure up to the expectations and in compliance with building codes.

Environmental engineering

Environmental engineering deals with the treatment of chemical, biological, and/or thermal waste, the purification of water and air, and the remediation of contaminated sites, due to prior waste disposal or accidental contamination. Among the topics covered by environmental engineering are pollutant transport, water purification, waste water treatment, air pollution, solid waste treatment and hazardous waste management. Environmental engineers can be involved with pollution reduction, green engineering, and industrial ecology. Environmental engineering also deals with the gathering of information on the environmental consequences of proposed actions and the assessment of effects of proposed actions for the purpose of assisting society and policy makers in the decision making process.
Environmental engineering is the contemporary term for sanitary engineering, though sanitary engineering traditionally had not included much of the hazardous waste management and environmental remediation work covered by the term environmental engineering. Some other terms in use are public health engineering and environmental health engineering.

Geotechnical engineering

Geotechnical engineering is an area of civil engineering concerned with the rock and soil that civil engineering systems are supported by. Knowledge from the fields of geology, material science and testing, mechanics, and hydraulics are applied by geotechnical engineers to safely and economically design foundations, retaining walls, and similar structures. Environmental concerns in relation to groundwater and waste disposal have spawned a new area of study called geoenvironmental engineering where biology and chemistry are important.
Some of the unique difficulties of geotechnical engineering are the result of the variability and properties of soil. Boundary conditions are often well defined in other branches of civil engineering, but with soil, clearly defining these conditions can be impossible. The material properties and behavior of soil are also difficult to predict due to the variability of soil and limited investigation. This contrasts with the relatively well defined material properties of steel and concrete used in other areas of civil engineering. Soil mechanics, which describes the behavior of soil, is also complicated because soils exhibit nonlinear (stress-dependent) strength, stiffness, and dilatancy (volume change associated with application of shear stress)

Water resources engineering

Water resources engineering is concerned with the collection and management of water (as a natural resource). As a discipline it therefore combines hydrology, environmental science, meteorology, geology, conservation, and resource management. This area of civil engineering relates to the prediction and management of both the quality and the quantity of water in both underground (aquifers) and above ground (lakes, rivers, and streams) resources. Water resource engineers analyze and model very small to very large areas of the earth to predict the amount and content of water as it flows into, through, or out of a facility. Although the actual design of the facility may be left to other engineers. Hydraulic engineering is concerned with the flow and conveyance of fluids, principally water. This area of civil engineering is intimately related to the design of pipelines, water supply network, drainage facilities (including bridges, dams, channels, culverts, levees, storm sewers), and canals. Hydraulic engineers design these facilities using the concepts of fluid pressure, fluid statics, fluid dynamics, and hydraulics, among others.

Materials engineering

Another aspect of Civil engineering is materials science. Material engineering deals with ceramics such as concrete, mix asphalt concrete, metals Focus around increased strength, metals such as aluminum and steel, and polymers such as polymethylmethacrylate (PMMA) and carbon fibers.
Materials engineering also consists of protection and prevention like paints and finishes. Alloying is another aspect of material engineering, combining two different types of metals to produce a stronger metal.

Structural engineering

Structural engineering is concerned with the structural design and structural analysis of buildings, bridges, towers, flyovers, tunnels, off shore structures like oil and gas fields in the sea, and other structures. This involves identifying the loads which act upon a structure and the forces and stresses which arise within that structure due to those loads, and then designing the structure to successfully support and resist those loads. The loads can be self weight of the structures, other dead load, live loads, moving (wheel) load, wind load, earthquake load, load from temperature change etc. The structural engineer must design structures to be safe for their users and to successfully fulfill the function they are designed for (to be serviceable). Due to the nature of some loading conditions, sub-disciplines within structural engineering have emerged, including wind engineering and earthquake engineering.
Design considerations will include strength, stiffness, and stability of the structure when subjected to loads which may be static, such as furniture or self-weight, or dynamic, such as wind, seismic, crowd or vehicle loads, or transitory, such as temporary construction loads or impact. Other considerations include cost, constructability, safety, aesthetics and sustainability.

Surveying

Surveying is the process by which a surveyor measures certain dimensions that generally occur on the surface of the Earth. Surveying equipment, such as levels and theodolites, are used for accurate measurement of angular deviation, horizontal, vertical and slope distances. With computerisation, electronic distance measurement (EDM), total stations, GPS surveying and laser scanning have supplemented (and to a large extent supplanted) the traditional optical instruments. This information is crucial to convert the data into a graphical representation of the Earth's surface, in the form of a map. This information is then used by civil engineers, contractors and even realtors to design from, build on, and trade, respectively. Elements of a building or structure must be correctly sized and positioned in relation to each other and to site boundaries and adjacent structures. Although surveying is a distinct profession with separate qualifications and licensing arrangements, civil engineers are trained in the basics of surveying and mapping, as well as geographic information systems. Surveyors may also lay out the routes of railways, tramway tracks, highways, roads, pipelines and streets as well as position other infrastructures, such as harbors, before construction.
Land surveying
In the United States, Canada, the United Kingdom and most Commonwealth countries land surveying is considered to be a distinct profession. Land surveyors are not considered to be engineers, and have their own professional associations and licencing requirements. The services of a licenced land surveyor are generally required for boundary surveys (to establish the boundaries of a parcel using its legal description) and subdivision plans (a plot or map based on a survey of a parcel of land, with boundary lines drawn inside the larger parcel to indicate the creation of new boundary lines and roads), both of which are generally referred to as cadastral surveying.
Construction surveying
Construction surveying is generally performed by specialised technicians. Unlike land surveyors, the resulting plan does not have legal status. Construction surveyors perform the following tasks:

• Survey existing conditions of the future work site, including topography, existing buildings and infrastructure, and even including underground infrastructure whenever possible;
• Construction surveying (otherwise "lay-out" or "setting-out"): to stake out reference points and markers that will guide the construction of new structures such as roads or buildings for subsequent construction;
• Verify the location of structures during construction;
• As-Built surveying: a survey conducted at the end of the construction project to verify that the work authorized was completed to the specifications set on plans.

Transportation engineering

Transportation engineering is concerned with moving people and goods efficiently, safely, and in a manner conducive to a vibrant community. This involves specifying, designing, constructing, and maintaining transportation infrastructure which includes streets, canals, highways, rail systems, airports, ports, and mass transit. It includes areas such as transportation design, transportation planning, traffic engineering, some aspects of urban engineering, queueing theory, pavement engineering, Intelligent Transportation System (ITS), and infrastructure management.

Municipal or urban engineering

Municipal engineering is concerned with municipal infrastructure. This involves specifying, designing, constructing, and maintaining streets, sidewalks, water supply networks, sewers, street lighting, municipal solid waste management and disposal, storage depots for various bulk materials used for maintenance and public works (salt, sand, etc.), public parks and bicycle paths. In the case of underground utility networks, it may also include the civil portion (conduits and access chambers) of the local distribution networks of electrical and telecommunications services. It can also include the optimizing of waste collection and bus service networks. Some of these disciplines overlap with other civil engineering specialties, however municipal engineering focuses on the coordination of these infrastructure networks and services, as they are often built simultaneously, and managed by the same municipal authority.