British Guidelines for Providing Whisper Concrete

After development of whisper concrete in Belgium, no guidelines or specifications were not available for this exposed aggregate concrete finishing. After Belgium, many countries of this continent use this resurfacing method of providing skid resistance and noise reduction due to high speed vehicles. This method when used in United Kingdom, their also it becomes popular. But British engineers set guidelines to adopted whisper concrete. 

First we recall the whisper concrete finishing procedure, to understand the changes were brought in British guidelines. We will discuss this in brief in few words. A 40-50 mm thick concrete layer is provided over smoothened concrete pavement having a coarse-aggregate size ranging from 6-8 mm. While the concrete is green a retarder mixture of glucose, alcohol and water is sprayed on it and covered with polythene sheet immediate after applying spray. After 8-36 hours, the sprayed surface is swept and using special bristle brushes, top 1.5-2 mm is removed to form an exposed aggregate surface, named whisper concrete. 

Austria is also worked much with this resurfacing concrete finishing. British guidelines provide complete guidelines including sub-base foundation and main concrete pavement. The main concrete pavement is known as continuous reinforced concrete pavement (CRCP). 

Sub-base:

Under standard conditions-the sub-base should be cement based sub-base. The thickness recommendation is about (150-200) mm.

CRCP:

Over this sub-base a continuously reinforced concrete pavement, known as CRCP, is provided. The recommended thickness of CRCP should be 200 mm. we will discuss about CRCP in upcoming post.

Whisper Concrete:

Over the CRCP the whisper concrete is applied. The recommended thickness of whisper concrete is 50mm.

Now guidelines to construct whisper concrete:

1. Generally coarse aggregate of 8 mm size is recommended for this concrete surfacing.

Tolerance: 

Only 3% oversize of specified size can be accepted.

Only 10% undersize of specified size can be accepted.

2. A limitation on flakiness index is also provided. This should not greater than 25%.

3. Sand used in whisper concrete should be very fine

4. For a certain amount of concrete, the coarse aggregate should consist 60% of it.

5. Regarding retarder- there should be glucose, alcohol and water.

6. The spraying surface should be covered with polyethylene sheet.

7. The removal period of polyethylene sheet should be after (8-36) hours.

8. A mechanically rotating bristle stiff brush should be used to remove top concrete mortar

9. The depth of concrete mortar removal should be 1.5 mm

What is Jetting and Drilling in Pile Foundation Construction?

Jetting and drilling are the processes to penetrate a dense stratum which is to penetrate to continue the pile to a underlying soft depositions to make safe pile foundation. The dense layer may consist of gravel or sand and piling have to be continued as there have one or more weak strata beneath this dense stratum.

Jetting is used to facilitate penetration through a dense layer. Normally jetting loosens the dense soil deposit with the help of water. To achieve this, water is discharged with pressure near the particular point or along sides of pile. In this purposes a (2-3) in diameter pipe is used. Now we have to know the discharge rating and pressure of delivery water.

The pump that is used to jetting purposes must have a capability of developing 500 gallon per minutes with a pressure of (150-200) lb/sq.in. Our aim is to create quick conditions. When the loosen sand undergoes quick conditions, the penetration of pile through these dense sand or gravel becomes easy and piling can be continued to underlying weak soil deposit.

But when the layer found is very stiff and strong then foundation engineers have to think about other method of penetration. Yes we are talking about rotary drilling. Rotary drilling is capable to penetrate the before said dense layer and even more stiff or harder cohesive soil up to a considerable depth.

The rotary drilling was first 3000 B.C. in Egypt. The Leonardo Da Vinci in 1500 developed an image that resembles to recent rotary drilling techniques. In rotary drilling a sharp drill bit with rotating facility is used to dig hard soil deposit. This is a bit like a hand drill. We have published post regarding drill bit. The spinning action of dtill bit has capability to penetrate even hardest rock. This technique not only used in piling operation but also it is frequently used in petroleum industries where thousand meters of drilling is generally required.

Unsupported Foundation Excavation in Clay Soil

In the previous post we have learned about foundation excavation in sand without any support to the slope. We learned these that sand have little cohesion and these soil is unstable in steeper slope. we have provided some regular slope for sandy soil excavation. But question is clayey soil is a cohesive soil. Is it safe to excavate this soil unsupported and can be left open for considerable period. We will find the answer of this question in this post.

Normally, foundation engineer proportions and designs foundation for given superstructural loads. This is not function of engineers to select excavation equipment for a proposed site or to provide bracing. The foundation construction of any locality normally excavates and provides support to excavation if required.

However, engineers have to approve the construction procedure, in this fact excavation procedure and safety, for a given construction site. But for a giant project it is required to provide construction guidelines from design office.

Now we will discuss the facts with clay soil. We will learn about the factors that control to provide a steeper slope:

1. Depth of cut

2. Shear resistance of desired clay soil.

Now we have to notice the properties of clay below base level of foundation excavation. If it is soft, a flat slope is chosen. This is done to avoid rise of bottom. Now we will consider hard or stiff clays. Normally this type clay commonly has cracks or develops crack, near ground. Have there any problem with cracks? 

 Yes this weak joint of clay soils are penetrated by water, a hydrostatic pressure is developed and which may lead to failure of slope even in stiff clay excavation. This pressure reduces the factor of safety considered in providing a steep slope.

With the time the moisture penetrated further deep in the excavation sides’ results soft clay (previously stiff). This also reduces factor safety with time. So one should not thick an excavation in clay deposit is unquestionable.

It is possible to provide steep slope and this slope remain stand satisfactory in clay soil for certain periods. But considering above fact, it is very common to provide support to excavation in clay type soil too for a safe and sound construction progress in foundation engineering.

How Lightweight Concrete is Compacted with Vibrator?

Dear reader we are on very old blog. We are posting articles on concrete construction and foundation engineering with their repair technologies. We have publish many post regarding concrete compaction, both hand compaction and mechanical compactions. Now in this post we will discuss additional requirements for vibrating lightweight concrete. We will provide a table that has links for all posts on concrete and concrete compaction.

The recommendations that are valid for normal weight concrete compaction also valid in compacting lightweight concrete with some additional observations and precautions. Now we have little idea about lightweight concrete.

From the name we can understand, the concrete must be lighter than normal one. Generally, application of lightweight aggregate in concrete makes it lighter.

The aggregates are derived from following sources:

a. Treating raw materials say slate, clay or shale. There heat treatment is used.

b. Volcanic pumice

c. Manufactured from the by-products of industry like flyash

d. Processing by products formed from industry such as slag or FBA

Concrete weight can be reduced by many other ways. But if the resulting concrete has lighter weight, we can take it as lightweight concrete, in general.

Dear reader lets come to the point compaction. We have published several posts on lightweight concrete and promised to post further topics regarding this.

As aggregate weight is less, there have a tendency of this aggregate to come out to surface in fresh concrete. This tendency is maximized by the action of over-vibration to concrete mass. To avoid an undesirable segregation, a concrete of fairly stiff mix is designed to have minimum requirement of vibration in consolidating concrete mix in forms. We provided that stiff mix-not a too wet mix. In very wet concrete mix, having over-vibrated, the raised coarse aggregate to the surface, results difficulties in finishing. We have published several posts on over-vibration with images taken from different site. You can extract information from these posts.

Performance of Whisper Concrete

We have already discussed about hydroplaning. To avoid noise and possible loss of control of vehicle, time to time, it is required to regrooving existing worn smooth concrete pavement surface. We have mentioned earlier that regrooving and resurfacing on concrete are the method to provide skid resistance of vehicle. Here we will discuss about performance of a resurfacing method and compare it with regrooving method.

We have learned earlier that regrooving on concrete pavement is costly and a quite laborious work. This practice may also have risk is missing some area or some section of pavement surface. Instead of this grooving we have recommended to apply resurfacing. We have discussed a special type of concrete resurface method. For details please what is whisper concrete.

Being discovered in Belgium authorities (who have named this type of finishing of resurfacing concrete as whisper concrete), many countries of the world have adopted this surfacing method. Now we will learn why everyone adopted this concrete finishing.

Firstly, the highway engineers have analyzed the cost effectiveness of this surfacing. They found that providing a 40-50 mm concrete layers over defected (smoothen) concrete pavement, results quite small difference in cost, if they used regrooving method. 

Secondly, whisper concrete renders a white topping which is expected by the engineers.

Third factor is noise reduction, we will discuss about noise reduction in the next post. United Kingdom adopted this technology in 1995. They have developed some guidelines for providing a quality and cost-effective whisper concrete that also reduce noise level. Thus whisper concrete had entered in some codes and standards. We will learn these guidelines in the next post. Please stay with us.

High Density Polyurethane Foam form EFT for Raising and Repair of Concrete Slab Foundation

We everyone knows that replacing a concrete slab foundation or concrete pavement is very costly attempt to rehabilitate a distressed or sunk concrete slab. Besides replacing, slabjacking can provide cost-effective solution, reducing also the cost half of that replacing. In some areas, where removal and demolition of concrete is tough, in odd situations, where service and repair have to be done simultaneously.

Leaving behind traditional mudjacking (slab jacking with regular cement grout), Engineered Foundation Technologies (EFT), have brought to foundation engineers a magic solution with polyurethane foam. They got very good reputation in New England and some other states with that their successful polyurethane injection methods.

So far they have successfully conducted repair and rehabilitation of slabs that rest on ground. The scopes of their application are:

a. Concrete ramps

b. Side walks

c. Concrete pations

d. Concrete road pavement

e. Driveways

f. Foundations

g. Garage floors

h. Parking lots

i. Industrial floors

j. Basements

We will publish numerous post regarding basement water proofing in this blog. Please stay with us.

EFT serves a high density injection foam containing polyurethane, effectively lift and stabilize slab foundations or concrete pavements. Now why we should use this polyurethane injection?

Answers are-

1. Using it we may avoid costly demolishing and hazard related to demolition.

2. Business or traffic movement can be operated smoothly around the restoration area

3. The service areas become usable within 15 minutes

4. It is light in weight and does not produce over burden pressure from newly applied materials.

These are the points which make EFT’s methods superior to traditional slabjacking with cement grouting. Imagine only four pounds weight of polyurethane can replace 140 pounds of conventional cement grout to fill a cavity beneath a distressed slab. With a lighter weight it provides strongest lifting technology of concrete member.

We have missed an important advantage. This is high density polyurethane application even under water or the repair area which is wet, provides chemical reactions as that reacts in dry conditions. The repaired area becomes water resistant and provides a moisture barrier in penetrating into the concrete slab.

How are Air Voids Provided in Concrete to form Light Weight Concrete?

We have learned about light weight concrete and different aspects of it and the aggregates that render lighter properties to concrete. Here we will learn how it becomes light. It is very easy to understand that weight of a material or a material that formed by different constituents can be reduced, if solid content can be replaced by air voids to some extent. The replacing amount depends on the required density i.e. weight of materials to be achieved.

As discussed above we need to replace some solid content from concrete. We know concrete is composite materials consists of natural admixtures. Now question is from which we will replace solid content.

We can replace solid contents from three probable locations, in other word; we can provide air void in three probable locations. They are:

a. Providing air void to aggregate particles and this aggregate are called light weight aggregate. The resulting concrete is called light weight aggregate concrete.

b. Providing air in cement paste. This result a concrete called cellular concrete. We will discuss about cellular concrete in the very next post.

c. Providing air void between coarse aggregates omitting the fine aggregate in concrete mix. This concrete is called no fine concrete.

So light weight properties can be brought to concrete in providing voids in these three probable entrance locations. Depending on air entrance this concrete becomes light but have different physical properties and mechanical properties. We will discuss about all verities of lightweight aggregate and light weight concrete as well, in details in upcoming posts. We have already introduced leca-a light weight aggregate in last post. Please stay with us.

Leca: The best light weight Aggregate for Thermal Insulated Concrete

As some construction process in particular cases concrete unit need to be light and thermal insulated. With the reduction of weight of concrete structure, Leca provides a great thermal insulated concrete. Leca is nothing but light expanded clay aggregate, brings to us by LECA Building Material Trading .

A lightweight concrete decreases weight of structure significantly. Thus reducing the member size, it brings economy to construction industry too. We have published several posts about light weight concrete. Here we are discussing a particular product that were discussed before briefly or accurately just used this brand name as an example of treated aggregate category.

The lightness of concrete is a headache to engineers as a lighter structure induces lesser earthquake forces. Now we will know about Leca. Numerous small, puffed and lightweight particles form Leca. It is derived by burning clay. It has numerous cavities filled with air. These cavities render strength and insulation properties to Leca.

The basic material of Leca is plastic clay which is heated in rotary kiln, after pre-treating them extensively. These heated materials get expanded and produce finished product Leca. The temperature at which it is burnt is 11000C. Leca is environment friendly product; it is non-conbustible, impervious and free from attack from insects, we-rot, dry-rot.fff

Test performed according to EN12667 the following results regarding co-efficient of thermal conductivity are found:

These results depicts that Leca is high quality thermal insulation aggregate and produce light weight high thermal insulated concrete as well. Regarding weight 800kg/cum is very light. Using this product in concrete construction unit (like partition wall), saving both fuel and electricity consumption. Thus building steps ahead to be a green building. Dear readers please stay with us we will provide introduction to such building materials that makes a building energy efficient.

What is Whisper Concrete?

Dear reader this is also a new term at least to me, you may have known about it. This concrete is developed in Belgium. We have published earlier about hydroplaning in concrete pavement. You may have read this post. Our aim is to make concrete pavement more skid resistance but reducing noise level. We will now provide a method of resurfacing of existing concrete pavement that get smoothen by the action of tyres of heavy traffic on road surface. Re-grooving is provided sometimes to roughening the road surface. Grooving in this manner is very costly and need hard working to achieve this.

 

Belgium is pioneer to reduce noise pollution due to high speed traffic movement, instead of re-grooving they made another effort-exposed aggregate finish. The exposed aggregate finish is done by laying (40-50) mm concrete layer for resurfacing. The aggregate chosen as coarse aggregate is of (6-8) mm size. this is not new in resurfacing trend. The specialty is spraying glucose retarder, water and alcohol and being sprayed polyethylene sheet is used to cover the surface. One important thing we have missed-that is the timing of application of retarder mixer. They are sprayed while new concrete is green.

The road surface is washed out with special Bristle brushes. The brushes should be stiff with rotating facility. The sprayed surface is left covered for 8-36 hours before washing work.

The unset top mortar is removed up to a depth of (1.5-2)mm removed leaving aggregates to expose. This renders pavement surface a rough texture that is enough safe for high speed vehicles but still producing less noise. This concrete surfacing is called whisper concrete that we are hunting through this post. We will discuss mor e about whisper concrete in upcoming post.

What is Hydroplaning in Concrete Pavement?

Dear reader this is relatively new term to us and we suppose to you too. During reading a journal about concrete pavement problems, we found this term. New term is always an interesting thing to reader and to us too. Dear reader we have promised to give you every definition, every causes and every solutions for concrete problems in this blog. We are developing our blog structure to be surfed easily and to get relevant posts with enclosed with a desired post, have been reached by reader. You can discover post on concrete, foundation, foundation repair and we also publish tutorial on STAAD.Pro, ETABS and so on.

Lets go to the main point-hydroplaning. Concrete pavement becomes popular from many years and this term also produce problem to people for many years. Now-a-days a speed of 120 kmph is not uncommon in Europe and United States. The vehicle travels in this speed produce noise. The frictional sound between road surface and tyres produce this disturbing sound. In Europe people living near the roads, cannot tolerate this sound-this is really intolerable and regarding vehicular traffic volume, millions of vehicles travels on these highways.

In Europe, Belgium first took attempt to reduce the noise pollution. We know, when a new pavement is constructed, texturing is done by brooming or any other means to facilitate skid resistance. As vehicles travels over this road surface, it get worn out and becomes smooth. The water pool that formed on smooth concrete surface causes so called hydroplaning and high speed vehicles lose control and struggling with skidding and results accident.

Usually concrete roads need to be resurfacing or sometimes roughening in routine in interval of some years. The roughening is done by re-grooving. For many aspects of re-grooving and resurfacing of concrete surface, please stay with us. We will discuss every topic in this blog regarding concrete and foundation engineering.

Distressed Slab-On-Grade Foundation Raising by Polyurethane Foam Injection

Many foundations rest on slab that cast directly over ground. In commercial and industrial floors, the distressed slab by sinking, create many problems. It interrupts the functionality of a warehouse floor, when vehicular movement is necessary to enter and exit of goods. 

It also produces aesthetic and hygienic problems to the floor slab. In most industrial floor forklifts are very common to move around the floor. The repair of this slab is also expensive.

We have already discussed about injection method of cement grout for these purpose. Here we will discuss about another injection materials-its polyurethane foam. This type of material is very light weight, have short hardening period, leaving distressed slab to be repaired and serviceable within few minutes, even under the loading of heavy traffic or industrial forklifts.

Now we will discuss about the properties that make polyurethane foam a supreme injection material. We will discuss about setting time of it, in this post. We will finish this topic in the next part, where rest properties will be discussed. Here in some properties we will compare it with conventional mudjacking/slabjacking. You can read our posts on these traditional methods of repairing slab foundations.

a. Setting time:

This is important to make slab serviceable within few minutes, in very busy industrial or commercial floors, so that no interruption in shipment of goods or no hamper in regular service in a work station is occurred. Polyurethane foam serves this purpose accurately. Think within few minutes the floor is ready to serve. This is due to the super fast hardening properties of polyurethane foam-this is at most 15 minutes. 

Light Weight:

Now we will have idea about density of usual cement paste and polyurethane foam. The conventional cement grouts have weight around 150 lbs/cft whereas the polyurethane foam have density merely (2-10)lb/cft. As self weight of repair material is less, it produces overburden pressure, to soil beneath, of minimum value. This is also a very important factor to choose this material as repair and raising material.

Narrow Injection Holes:

In case of slabjacking the holes drilled to inject grout is around 1.5 inches whereas this foam requires mere 5/8 inch holes. Not only in hole diameter but also the foam have advantage over hole spacing. The injection holes required to penetrate foam is much further than of a slabjacking process.

Handling and Cleaning:

This work is much neater than grout injection. Being finished the injection of foam, the worker can pack up there instruments and materials very quickly i.e. demobilization time is less. Here in this process the cleaning operation for equipment is not required. Thus he work site can be left open for service without interrupting service area.

Insulation:

Polyurethane foam provides good thermal insulation too which produce a repaired area of not susceptible to extreme heat or extreme cold condition.

Moisture Retardation:

Closed-cell polyurethane results a repaired surface, that restricts or act as barrier to moisture to penetrate through the concrete slabs. This property is particularly important where expansive soil lies beneath pavement or slab.

What is LightWeight Concrete?

Now-a-days there have a tendency to provide lighter structure with the development of concrete technology. The lighter the structure, the less earthquake impact the structure suffers. As ground acceleration comes from seismic waves, converts to force with the weight of structure. The structural engineers, who analyze structure for seismic load, know about seismic dead load. We will not go to that point. This tendency of production lighter concrete brings forth light weight concrete.

At first we will provide the ranges of density of lightweight concrete. A density ranging from (300-1859) kg/cum can be achieved by light weight concrete. There a relationship between density and strength of concrete. 

So a very light concrete never produce a concrete to be act as structural member. Structural lightweight concrete should have density ranging from (1350-1900) kg/cum. The compressive strength of structural lightweight concrete should not less than 17 Mpa.

Weight reduction is done by using

1. Light weight aggregate

2. Foamed concrete

3. Autoclaved aerated concrete

We will first learn about light weight aggregate. We can collect this aggregate from both natural, artificial and sometimes from the by-product from industries. The sources of aggregate are from:

a. Natural sources:

volcanic pumice

b. Industrial by product:

1. Fly ash is the very common by-product of industry. As an example, Lytag has been using over 40 years as lightweight aggregate. It is light, strong, consistent and environmental friendly too. It complies with EN13055.

2. Slag is also a processed by-product of industry. Furnace Bottom Ash (FBA) is found from power stations that use coal as fuel. Its size may vary from fine grained sand to gravel.

c. Artificial or treated: 

treated with temperature, clay, shale or slate can be used as light weight aggregate. Example: light expanded clay aggregate (LECA). This is formed by burning clay. It has numerous cavities filled with air. This makes it light and thermal insulator as well.

Dear reader we will publish posts regarding the lightweight aggregate in details. For learning foamed concrete and autoclaved aerated concrete, please read next few posts. In the very next post you will find important` information about LECA.

Stress Reduction: A Method of Rehabilitation of Concrete Building

So far we were on different methods of rehabilitation and repair of concrete structure or its specific members to make it serviceable for further use and upgrading its capacity for higher occupancy classifications. We have published different methods of repair and concrete repair materials as well. We will publish more methods of repair and advance repair materials to upgrade a structure with repair.

Now here, in this post we will discuss a method of rehabilitation, that doesn’t need repair work or further construction of new structural elements. This method requires some forms of dismantling just to make it serviceable by reducing stresses in the structure itself.

This method provide a relief to structure that are distressed or evaluated as hazardous for upcoming any disaster like earthquake or tornadoes or unexpected loading from any other sources. This is achieved by doing following stress reduction work:

a. Reducing some dead loads and live loads by changing occupancy classes.

b. Sometimes lightweight partitions are chosen to replace heavy weight partition of solid forms. Now-a-days many lightweight materials for partition wall are developed and used in practical cases to achieve this purpose for both new and older structures, rehabilitates in such manner.

c. Providing open spaces in floor by removing inside filler walls. This can be done only when occupancy class is changed.

d. A method of reduction can be imagined easily is reduction of stories. This provides a great amount reduction in stress and provides a safer column and shear wall if there have any.

e. A lower loading classification can be considered like avoiding some storage facilities, removing or reducing facilities of library, avoiding assembly places in the structure to reduce live loads.

f. Span of beams of structure can be reduced by applying struts etc.

Providing joints of shear movement in location of zero moment in continuous spans of structure is also a good method.

Epoxy Mortar for Concrete Repair

We have discussed different method of repair of concrete member in the previous posts. In the last post we have discussed about surface preparation method for providing repair materials. Now we will discuss another method of concrete repair and its application for particular cases.

At first we will learn which components forms this special mortar:

a. Resin

b. Hardener

c. Silica sand

This component with epoxy bonding coating provides a mortar that can repair old concrete surface.

The special advantage provided by this mortar is:

a. High strength

b. High abrasion resistance

c. Water resistance

d. Having facility to apply in thin film of few millimeters.

Now we will learn in which locations/conditions this mortar is essential. They are

1. Where concrete bonded with epoxy can not be used due to accessibility problem.

2. Where repair work required less than 40 mm thick overlay of repair mortar.

3. Where a small quantity (No.) of point or small area have to be repaired. This is practical for less than 0.1 Sqm.

We have mentioned earlier that this mortar is applicable when patch thickness is less than 40 mm. But when the required thickness exceed 15 mm and patching work have to cover large areas then patching work done in layers providing mesh reinforcement fixed with the help of U-nails or sometimes by shear keys.