Specification for Corrosion Inhibition and Bond Breaker for Micropile Foundation

We know corrosion is very important factor for subsurface construction and sometimes becomes governing factors in pile construction depending on ground condition. Dear reader we have already discussed about measures to be taken for corrosion protection of micropile.

Corrosion inhibition, if required, the compounds used for this purposes in free length and should be of organic say wax or grease.

The inhibiting compounds should have

Corrosion protection in micropile, Skyline Steel, Nucor Corporation

• Self-healing behavior

• Inhibiting additives

• Appropriate method for displacing polar moisture

• Nonreactive with

• Prestressing steel
•  Anchor grout
•  Sheathing materials

• Chemically stable

• Can permanently retain its viscosity

When bond breaker is required, smooth plastic pipe or tube should be used for fabrication of it. The expected properties of pipe or tube are as follows:

• Should have resistance against chemical attack; the aggressive environment, corrosion inhibition or grout are considered to produce chemical attack.

• Should have resistance against aging from UV-light

• Not harmful to any type of reinforcement

• Should have ability to withstand

• Impact
• Abrasion
• Bending while handling & installation

Regarding application of bond breaker, we can include, it allows elongation of prestressing steel while testing and also stressing. The tube or pipe discussed above should be made from polyethylene of medium-high density and should conform

• ASTM D1248

• AASHTO M252

Sometimes of polyvinyl chloride (PVC) tubes/pipes are uses which should comply with ASTM D1784, class 13463-B having wall thickness of at least 0.04 in or equivalent materials can be used.

Milling Methods for Concrete Removal to be Repaired

In concrete repair work usually damaged, deteriorated or defective portion have to be removed and in most cases damaged portions are hardly defined. Most recommendation state that deteriorated or damaged material must be removed completely.

It is very difficult to determine that all such portions are removed or excess amount are removed (i.e. some sound concrete is removed). A recommendation is to continuing removal until aggregate (coarse aggregate) particles are broken down under removal process instead of removal of cement matrix (which is relatively simpler than breaking down of aggregate).

But when low strength concrete is damaged, the aggregate may never fractured under demolition. Here we will learn about milling methods of concrete removal. This method is suitable for removing concrete from both vertical and horizontal surfaces; especially when specific amount from large concrete member.

The depth of removal may range from 3 mm to 100 mm approximately. This method usually produce sound concrete surface free from microcracks.

Usually scarifiers are used in these purposes. It is a cutting tool that uses rotary action with its mass of cutter bits. The rout cutting into concrete surface removes loose fragments of concrete like scaling from blasted surface. Weakened concrete (by any expansive agent) or previously cracked concrete can be successfully removed by this method.

Scarifiers of various sizes are available. Other advantages of this tool are:

• Controlled removal of concrete to defined limit.
• Simple in operation
• Debris produced is relatively small which can be handled easily.
• Both sound and deteriorated concrete containing wire mesh and ties (from formwork) can be removed.
• Applicable for decks, slabs and for mass concrete.
• Broom-mounted cutters can be used to remove concrete from ceiling and walls

Some limitations are as follows:

• Concrete with reinforcement cannot removed
• Removal rate becomes very low when applied to sound concrete
• Noise, dust and vibration are produced
• Concrete having microcracks can be damaged.

Effect of Accidental Inclusion of Sugar in Concrete

We know many impurities in water used in concrete mix produces different affect on concrete properties. Deleterious substances may also be included in concrete through aggregate (both fine and coarse aggregate). Here we will learn about effect of sugar in fresh concrete.

Though the title of this post is accidental application of sugar in concrete but in some important projects sugar is used intentionally for specific purposes. Sugar has retarding influence on concrete. Now consider about accidental inclusion; sugar mainly included due to use of sugar bags to transport aggregates to laboratory or when fresh concrete is transported by molasses bags.

This effect was discovered when investigation was conducted for very low strength of lab sample with proper mix design, careful sampling and curing procedures. The effects depend on quantity of sugar used/included and confusing results were found in previous tests.

It was found that careful application of sugar in small quantity resulted satisfactory retarding effect. The dose and retarding effects are as follows

Dosage: 0.05% of cement (measured by mass)

Retarding effect: about four hours

The probable cause of retardation is preventing action of sugar to form C-S-H. But actual rate of retardation depends on chemical composition of cementitious materials. Like other retarder, for this reason, performance of sugar as retarder should be ensured by different trail mixes (with actual cement that will be used in this job).

Sugar, thus, can be used in many untoward situation like when mixer or in some cases agitators become out of order and concrete cannot be placed due to site condition. The important fact is that it is an inexpensive retarder. Molasses was applied in construction of channel tunnel when residual concrete was required to be retarded due to difficulty in washing out underground.

Channel tunnel was constructed between Folkestone, Kent, England and Coquelles, Pas-de-Calais, France. The tunnel was opened on 6 May 1994. Construction began in 1988 and our reference was in 1990. A dose of (0.2-1) % of cement (by mass) will actually prevent total setting of cement.

Now we have to know about final strength of concrete on this application. When this retarder is applied in controlled manner, obviously, early strength becomes very low but after 7 days, the strength is increased by several percent relative to mix that are not retarded. The probable cause is hydrated cement gel becomes denser due to delayed setting.

Handling Precaution of Concrete Aggregate

We are very conscious about handling of concrete; in most cases don’t pay head to handling of aggregate. Handling of aggregate is also important to have designed gradation, to avoid foreign materials in aggregate and also to have ease of batching and economy of the same too.

Stockpiling and handling of coarser aggregate can lead to segregation. While tippling and discharging aggregate usually rolls down along slope. The large size aggregates have more weight and smaller size aggregates are relatively lighter. Thus large size particles remain in the bottom, the lighter particles remains at the top.

These results uniform grading at all layer; following size fraction should be spitted

 3/16” to 3/8”

 3/8” to ¾”

 3/4” to 1½” etc.

Splitting means stockpiling and handling separately; can be remixed during feeding into concrete mixer according to desired proportions. Even after this precaution segregation can be occurred but would be in narrow range within each fraction and even careful handling can reduce this segregation.

When aggregate particles to be handled are greater than 1½ in; there have every possibility to breakdown large aggregate particles. The precautions should be taken in this case are:

 Using rock ladders to lower aggregate into bins

 Not to drop from height.

In important and large projects, extra precaution to avoid breakage and segregation of aggregate is taken by providing rescreening just before feeding into bins. Thus excess of undesired undersize particles are eliminated.

Rescreening controls proportions of various sizes of aggregate effectively but with greater control more cost and complexity of batching operation are added.

Again a denser pack of aggregate leaves less space to take place finer cement particles; thus requirement of cement or cementitious materials are reduced and eventually economy is added against more cost of screening.

The uniformity of concrete also produces more workable mix facilitating placing. Again improper handling can cause contamination by deleterious substances and also by aggregate of low strength, less durable and undesired sizes. Sometimes aggregates are transported by contaminated container or sacks like sugar or salt etc. The affect of presence of salt in concrete has already been described in previous posts and in upcoming post we will learn about effect of adding sugar to concrete.