What is Microsilica?

Microsilica can be used in concrete and refractory materials. Microsilica ,when used in concrete, it can improve concrete’s properties such as compressive strength, bond strength and abrasion resistance, reduces permeability,and therefore helps in protecting reinforcing steel from corrosion. At the same time, Microslica can still be used in the procustion of refractory and porcelain, to raise intensity and durability, it also can be used in paint, coating resin rubber and other high molecular as a filler material to improve the material overall performance.

Use of Microsilica concrete

• Increased strength – faster construction, better design,reduced volume.

• Reduced permeability – more durable, less chance of gaseous escape, less attack from chemicals.

• Reduced cement content – use of SCMs.

• Reduced heat – less cracking.

• Greater lifetime – less repairs, greater security

• Better economics and a safer construction.

Microsilica concrete in  Civaux ll Nuclear power plant, Poitiers, France.

Microsilica is used in concrete for the double wall linings. The Inner wall is prestressed and outer wall is reinforced where Inner wall contains any radioactive release in case of a catastrophic failure.

PD-1 CONTINUOUS PRE-DAMPENER FOR SHOTCRETE APPLICATION

Designed to be used with packaged, pre-blended materials for shotcrete applications in Refractory, Underground and Civil applications, the PD-1 Predampener allows the addition of a controlled amount of moisture to bagged material as it is transported and fed into the gun. Pre-dampening eliminates static electricity while greatly reducing dust, rebound and gun wear parts. Most importantly, pre-dampening produces the highest quality of in place material.

Technical Data
Industries	Refractory, Und-erground, Civil	*
Process Type	Dry
Output	-
Distance	5 hp (4kW) 3/60/230/460 electric
Power	-
Mounting	-
Weight	1,400 lbs (635kg)
Dimensions	106" (2,692mm) x 56" (1,422mm) x 72" (1,829mm)
Options
Power	Air mortar, hydraulic mortar
Mounting	Trailer, skid
Special	-

What is Rebound in Dry-Mix Process in Shotcreting?

If you were to research the American Concrete Institute or the American Shotcrete Association, you would find that both terms refer to the application process of good old fashion concrete. The concrete mixture travels from an applicator’s truck to the site via a large hose. Air pressure is applied and the mixture is “shot” into place at speeds approaching 200 mph. This is extremely important! Why? Because it is with the forced placement of the concrete that either process gains it’s merit. Any concrete placement should be “compacted” to remove voids, air bubbles that weaken the strength of the eventually hardened concrete. For concrete that is poured, applicators will use a variety of methods, tamping, vibration, etc, to achieve compaction, but no process by hand can compare to the compaction that can be achieved by the pneumatically applied shot-crete or gunite.

 Rebound Safety of  Shotcrete: Safety Equipment, Including Facing Shields or Goggles, Respiratory Protection and Waterproof Gloves.

Now what is “rebound”? Rebound refers to the aggregate, which bounces or deflects off of the receiving material and lands in areas other than intended. When the small piece of sand is in mixture, it is combined with the moisten cement and if properly placed will added strength to the structure. If on the other hand, bounces off something hard, such as the wooden form or a piece of the steel reinforcement, the cement is likely to adhere to the hardened surface, but the sand, now mostly stripped of the binding agent falls elsewhere. This rebound, must be gathered up and removed, not allowed to become part of the structure. To do so would be to create a weakened structure. It is known that the dry-mix process creates substantially more rebound than the wet-mix process. If the applicators are skilled in the process this deficiency can be overcome.

N-TYPE PNEUMATIC GUN: A Cement Guns Built By Allentown

Allentown’s “N” type guns are modern version of the original cement guns built by Allentown for more than 95 years. They remain the most versatile machines available for the complete range of dry-process gunite in Refractory and Civil applications. They are ruggedly built to withstand hard, continuous use and are renowned for their ability to feed dry or damp, coarse or fine, and dense or lightweight materials at a smooth, accurately metered rate over 500 feet vertically and 1,000 feet horizontally.

xxTechnical Data
Industries	Refractory, Civil
Process Type	Dry
Output*	2 - 8 yd³/hr (1.5 - 6.1m³/hr)
Distance	1,000'+ (304m+) horizontal, 500'+ (152m+) vertical
Air Requirements	250 - 900 cfm
Rotor Speed	-
Weight	1,220 lbs (553kg)
Dimensions	46" x 46" x 54" (116cm x 116cm x 137cm)
Options
Power	Air motor, 2 -14 rpm (standard), 1 - 7 rpm hydraulic motor (when rig mounted)
Outlet	1.25" (32mm), 1.5" (38mm) (standard), 1.63" (41mm) and 2" (50mm)
Rotor Options	-
Hopper Options	-
Mounting	Steel wheels (standard), A-frame, forklift, rig
Special	Air-operated exhaust (standard), feedwheel cover, bag breaker

Revision for the ACI Shotcrete Nozzlemen Specifications

Many specifications are in need of revision because they do not require any level of nozzleman qualification, and some need revision because the qualification they require is outdated. The ACI Shotcrete Nozzlemen Certification program is the latest product of the ongoing initiative to promote certification of shotcrete nozzleman, originating with ACI Committee 506’s initial development of its “Guide to Certifying Shotcrete Nozzlemen,” ACI 506.3R, first published by ACI in 1982. Until the release of the current program, this document was the sole source of information guiding the qualification of shotcrete nozzlemen to ACI standards, and performed a crucial function for the industry while the formal program was under development—for their foresight, ACI Committee 506 is to be commended. However, with inception of the current program, ACI 506.3R effectively became obsolete because the process it describes allows a greater degree of latitude to the certifying agency in its content and administration, which renders it less standardized and more subjective than the current ACI program. Unfortunately, ACI 506.3R has not yet been withdrawn and is still being specified and recognized by individuals overseeing project requirements.
 
The retirement of the ACI 506.3R in its current form is imminent, as ACI Committee 506 is proceeding with action to formally withdraw the document so specifiers can replace reference to it in job specifications with reference to the ACI Shotcrete Nozzleman certification program. An appropriate citation may be “Any individual applying shotcrete must be certified as an ACI Shotcrete Nozzleman by the American Concrete Institute as outlined in ACI Certification publication CP-60.” Additional consideration should be given to whether the specification should state the type of process and/or the appropriate orientation of the test panel, for example: “Any individual applying shotcrete must be certified as an ACI Shotcrete Nozzleman Wet Mix Process Vertical & Overhead by the American Concrete Institute as outlined in ACI Certification publication CP-60.” Once included in the project specifications, the professional responsible for overseeing compliance with the specification should also identify and incorporate a mechanism by which the requirements are enforced on the job site. 

The ultimate success of this industry initiative to regulate itself is dependent on the cumulative and concerted efforts of the entire concrete construction community. ACI and ASA are committed to the continued nurturing, guidance, and delivery of the ACI Shotcrete Nozzleman certification program, and we realize that awareness and communication are our most effective tools.

Fly Ash Classification and Their Pozzolanic Properties

The Fly Ash is finely divided residue resulting from the combustion of ground or powdered coal. Fly ash is generally captured from the chimneys of coal-fired power plants; it has POZZOLANIC properties, and is sometimes blended with cement for this reason.

Fly ash includes substantial amounts of silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO). Toxic constituents include arsenic, beryllium, boron, cadmium, chromium, cobalt, lead, manganese, mercury, molybdenum, selenium, strontium, thallium, and vanadium.

Class F Fly Ash:

The burning of harder, older anthracite and bituminous coal typically produces Class F fly ash. This fly ash is pozzolanic in nature, and contains less than 10% lime (CaO). The glassy silica and alumina of Class F fly ash requires a cementing agent, such as Portland cement, quicklime, or hydrated lime, with the presence of water in order to react and produce cementitious compounds.

Class C Fly Ash:

Dumped Fly Ash in India

Fly ash produced from the burning of younger lignite or subbituminous coal, in addition to having pozzolanic properties, also has some self-cementing properties. In the presence of water, Class C fly ash will harden and gain strength over time.

Class C fly ash generally contains more than 20% lime (CaO). Unlike Class F, self-cementing Class C fly ash does not require an activator. Alkali and sulfate (SO4) contents are generally higher in Class C fly ashes.

In addition to economic and ecological benefits, the use of fly ash in concrete improves its workability, reduces segregation, bleeding, heat evolution and permeability, inhibits alkali-aggregate reaction, and enhances sulfate resistance. Even though the use of fly ash in concrete has increased in the last 20 years, less than 20% of the fly ash collected was used in the cement and concrete industries.

Four inch slump concrete made with Fly Ash

One of the most important fields of application for fly ash is PCC pavement, where a large quantity of concrete is used and economy is an important factor in concrete pavement construction.

What is Silica Fume?

Silica fume is By-product of semiconductor industry which was first ‘obtained’ in Norway, in 1947, when environmental restraints made the filtering of the exhaust gases from the furnaces compulsory. 

The terms condensed silica fume, microsilica, silica fume and volatilized silica are often used to describe the by-products extracted from the exhaust gases of silicon, ferrosilicon and other metal alloy furnaces. However, the terms microsilica and silica fume are used to describe those condensed silica fumes that are of high quality, for use in the cement and concrete industry.
 

Silica Fume consists of very fine particles with a surface area ranging from 60,000 to 150,000 ft²/lb or 13,000 to 30,000 m²/kg, with particles approximately 100 times smaller than the average cement particle. Because of its extreme fineness and high silica content, Silica Fume is a highly effective pozzolanic material. Silica Fume is used in concrete to improve its properties. It has been found that Silica Fume improves compressive strength, bond strength, and abrasion resistance; reduces permeability of concrete to chloride ions; and therefore helps in protecting reinforcing steel from corrosion, especially in chloride-rich environments such as coastal regions.

Solving Stormwater Problem Using Pervious Concrete

Pervious concrete contains a network of holes or voids, to allow air or water to move through the concrete. This allows water to drain naturally through it, and can both remove the normal surface water drainage infrastructure, and allow replenishment of groundwater when conventional concrete does not.
It is formed by leaving out some or the entire fine aggregate (fines), the remaining large aggregate then is bound by a relatively small amount of Portland cement.

When set, typically between 15% and 25% of the concrete volumes are voids, allowing water to drain.

The majority of pervious concrete pavements function well with little or no maintenance. Maintenance of pervious concrete pavement consists primarily of prevention of clogging of the void structure. 

In preparing the site prior to construction, drainage of surrounding landscaping should be designed to prevent flow of materials onto pavement surfaces. Soil, rock, leaves, and other debris may infiltrate the voids and hinder the flow of water, decreasing the utility of the pervious concrete pavement.

Mis-alinement Limitation of Bored Pile

Bore piles are the most popular and reliable deep foundation for heavy structures or less important or light structures founded on poor bearing strata. Bored piles are cast on the construction site which is normally of the order of 50 meters depth of drilling. The drilling depth and method is depending on the soil condition which is determined from soil investigation and decide suitable drilling technology. During boring there may have mis-alinement from the designed pile center.  

Off centering of bored piles in the vertical direction shall not be more than 1 in 200 of the bored pile length.

Offset from center in the horizontal direction shall not be more than 10 cm in any direction.

If any completed bored pile exhibit larger offsets than the above values, the Contractor must carry out corrective measure or construct a new bored pile as dictated by the Engineer all under the Contractor's own expense.

Cement Replacement Using Fly Ash in Pozzocrete

The Pozzocrete Fly Ash range is an artificial pozzolan, specially designed to achieve optimum performance on most cement and concrete applications. In the production of Pozzocrete 40™, 60™, 63™, and 83™ high quality PFA were selected and industrially processed in order to obtain maximum performance as a cement replacement product.The POZZOCRETE brand is reserved only for those grades which meet the Indian Standard 3812 , the European Standard EN450 Category S and the American Standard ASTM 618. Other by-products are called P... (with the related Grade number).

The process used to produce Pozzocrete Fly Ash significantly reduces the amount of unburned particles leading to a virtually carbon free material. Optimum reactivity is obtained by rejecting the less reactive crystalline Fly Ash particles and by increasing the specific surface of the final product.

The design of all Pozzocrete grades has taken into account the severe weather conditions in the areas where it may be supplied, in order to allow high cement replacement volumes insuring adequate strength development and good durability whilst avoiding short-term damage such as bleeding and thermo-hygrometric plastic shrinkage.

The use of this advanced pozzolanic Fly Ash material provides an effective reduction of the mixing water required and superior strength development, allowing high replacement rates that are not possible with normal cement additions. Compared to other Supplementary Cement Products Fly Ash in general and processed fly ash specifically provides changes to concrete in its fresh and hardened state. 

Effects of Supplementary Cementitious Materials on Fresh Concrete Properties

The use of this advanced pozzolanic Fly Ash material provides an effective reduction of the mixing water required and superior strength development, allowing high replacement rates that are not possible with normal cement additions. Compared to other Supplementary Cement Products Fly Ash in general and processed fly ash specifically provides changes to concrete in its fresh and hardened state.

Effects of Supplementary Cementitious Materials on Hardened Concrete Properties

Cement replacement

The cement replacement rate depends on cement and admixture type and on type of use. For normal concrete production using OPC, replacement rates in the range of 35% are recommended. For each single application the proper mix design shall be determined by appropriate testing.

The proper use of Pozzocrete results in long term technical improvements of the final product and at the same time ensures major cost savings to the user.

Packaging

POZZOCRETE products are available, depending on the product grade, in 30 kg paper bags, 50 kg HDP bags, Jumbo (big) bags carrying 1 – 1.3 ts , loose supply in 15 – 25 ts road tankers (bulkers) and on customer request in break bulk shipments.

The P-grades (with the exception of the P10 grade) are only available in big-bags or in bulker.

Cement-Related Parameters Controlling the Rate of Strength Gain of Concrete

Many parameters relating to the composition of the cement constituents and their proportions in the cement can affect the rate of strength gain and the final strength achieved. These include:

1. Alite content (Tri-Calcium silicates) & Belite contents (Di-calcium silicates) 

2. Alite & belite reactivity

3. Sulfate contents

Alite is the most reactive cement mineral that contributes significantly to concrete strength. More Alite should give better early strengths ('early' means up to about 7 days). 


Sulfate in cement, both the clinker sulfate and added gypsum, retards the hydration phase. If there is insufficient sulfate, a flash set (rapid hardening of freshly mixed cement paste with noticeable heat evolution) may occur. on the other hand too much sulfate contents can cause false-setting(rapid hardening of freshly mixed cement paste with minimum heat evolution) 

Some physical parameters of cement also play role in strength gain of concrete like Cement surface area and particle size distribution. 


Fineness is often expressed in terms of total particle surface area. More fine is cement; greater will be its hydration rate. Particle size distribution is also very important prospect in strength gain of concrete. Cement with very finely-ground gypsum and clinker particles results in slower hydration.

What is Wellpoint System for Foundation Drainage?

The wellpoint system is one of the most versatile of pre-drainage methods which can pump a few gallons per minute in fine sandy silts or many thousands of gallons per minute in coarse sands and gravels.

A wellpoint system consists of a number of wellpoints spaced along a trench or around an excavation site, all connected to a common header, which is attached to one or more wellpoint pumps.

Wellpoint systems are most suitable in shallow aquifers where the water level needs to be lowered no more than 15 or 20 feet. Due to the vacuum limitation of the pump, excavations that are deeper will require multiple stages of wellpoint systems.

When designing a wellpoint system, it is necessary to give first consideration to the physical conditions of the site to be dewatered.

Things to consider include:

-The physical layout

-Adjacent areas

-Soil conditions

Wellpoint system: A versatile of pre-drainage method

-Permeability

-The amount of water to be pumped

-Depth to imperviousness

-Stratification

To select the proper components of the wellpoint system - the friction losses developed in the suction side system must be considered.

When a Pile Said to be Damaged According to All Code?

Structure supported on soil which does not render adequate bearing capacity to support a heavy load (both moment and axial load) deep foundation is the only solution as shallow continuous foundation is economical. In this process bore hole are formed by suitable devices and concrete is poured around a reinforcing steel case. Due to some difficulties and some mistakes during piling some piles are considered as damaged pile. Bored piles are considered damaged when,

- The 28 days ultimate strength of concrete from the test specimens are below 27.6 MPa

- The concrete specimens cored from the finished piles show strengths below 27.6 MPa at 28 days, and the Engineer considered it defective.

- The length of bored piles do not met the requirements of the drawings or contract documents.

- The requirements according to codes listed below are not satisfied.

SI.	Requirements	Codes
1	Welding of reinforcing steel	AS/NZS 1554.3:2008
2	Concrete Structures Standard	NZS 3101 Parts 1 & 2:2006
3	Specification for concrete production	NZS 3104:2003
4	Methods of test for water and aggregate for concrete	NZS 3111:1986
5	Methods of test for concrete	NZS 3112:
6	Specification for water and aggregate for concrete	NZS 3121:1986
7	Steel reinforcing materials	AS/NZS 4671:2001
8	Design and Construction of Drilled Piers.	ACI 336.3R
9	Recommendations for Design, Manufacture, and Installation of Concrete Piles.	ACI 543R
10	Standard Test Method for Individual Piles Under Static Axial Tensile Load.	ASTM D3689
11	Standard Test Method for Piles Under Lateral Loads.	ASTM D3966
12	Structural Welding Code-Reinforcing Steel.	AWS D1.4

Damaged pile

- Tests show that bored pile cannot withstand the test loading equivalent to 2.5 times the design safe load because of defective piles which could have been resulted from collapsing of bored hole, impurities mixed into the concrete, bored holes being smaller than the specified sizes, inconsistent concrete strengths, and segregation of concrete mixture. In any case, the Contractor must be responsible for all payments to repair, or re-construct new pile as directed by the Engineer. Furthermore, the Contractor must be responsible for any additional expenses in making a necessary corrective actions to the entire structure such as expenses for "Tied Beams", "Micro Piles", "Enlargement of the Footing". In addition, the expenses involve in coring bored pile for concrete specimens, laboratory tests of the specimens, filling the core holes, and other bored piles repair shall be the responsibility of the Contractor if such actions are for confirmation purposes.