Leca Provides A Light Weight Concrete of Fire Resistant and Sound Insulation

We have already discussed about the light weight concrete and compaction recommendation for such concrete. Now we will discuss about an aggregate that provides excellent fire resistance and sound insulation.

We have known the name the Leca (light expanded clay aggregate). We have discussed about its thermal insulation properties. With thermal insulation it is also great way of insulating sound.

Leca is formed by burning it in rotary kiln at a temperature of 1100^oC. Before burning it was treated extensively. During burning plastic clay (base material) get expanded resulting a puffed internal structure of numerous cavities. These cavities are filled with air, that make it excellent sound proofing options to engineers.

Being environmentally safe, it is a great choice for green engineering construction. It is not susceptible to insect attack or dry-rot or wet rot. Leca aggregate and prefabricated concrete block is the best insulation material found in conducting test. A block of 10 cm width can fade 45 db and 15 cm width block can fade 46 db.

Regarding fire resistance it is also a material to fight well with fire. We have already discussed that it is formed by burning clay at 1100^oC. So it can resist fire about 3 hours. Here we are considering a block of 130kg/m³ density. 3 hours resistance against fire and fire spreading are a very important property for evacuation during fire hazard or to control fire by fire fighting equipments.

What should be the Slump of Concrete in Pile Foundation Construction?

In the last post we have discussed about working stress of concrete in pile. This post is related to this previous post. So have not published post about point bearing piles. We promise to publish it soon. Now we have learned range of working stress for cast-in-situ concrete piles. This working stress is expressed as a function of compressive strength of concrete at 28 days. Now we are providing some information about the slump of this concrete to reach this compressive strength. We know water content in concrete is designed in mix design depending on cement requirements in concrete and on many other factors. One of the other factors is workability. We have already published posts about workability and method to make concrete workable with plasticizers, superplasticizers or some other methods.

This workability is very important in concreting in pile foundation. We will not go to workability rather we provide some information about slump requirements for different types and different level of difficulties in concreting in pile.

A slump of (3-6)in. or more is suggested to obtain design concrete strength of piles that are cast-in-situ. Now question is 3-6 in. is a large range, what should be appropriate slump for your pile?

The answer is here-

For a smooth and straight pipe that is driven vertically, a slump of 3.5 in. can perform well.

For a pile that have difficulties in reaching concrete to tip of pile like vertical pile having heavy reinforcement or having corrugated shell or in case of batter piles, the slump value must be at least 6 in.

Dear reader we have published many posts regarding pile concreting. You are invited to read these. We promise to you that we offer or will offer quite vital information regarding pile concreting.

How Much Noise can be Reduced by Whisper Concrete?

We have already learnt about construction of whisper concrete. It was developed on Belgium. It is a special exposed aggregate concrete surfacing. There surface is brushed with special mechanical brush to expose aggregate to surface. These all are old things. Now we will go to the noise reduction. The exposed aggregate reduce contact surface between tyre treads and concrete pavement. Thus reduce noise with a roughened concrete pavement having greater skid resistance.

First it was surprised that when vehicles runs in high speed on whisper concrete surfacing, the noise level is reduced much than expected. In comparing to normal concrete surface it is revolutionary silent topping.

It is also found that the noise level is much lower than that on traditional black topped pavement. Some trails were done in construction process and engineers were confirmed that it really reduce significant noise. Then whisper concrete was used in many countries of this continent. In UK it was first used in 1995.

Traffic flow increases in recent decade and noise pollution also increased. Several environmental groups, throughout the UK, were campaigning to take measures to decrease the noise pollution by traffic. So UK took this factor seriously and they adopted whisper concrete from last 15-20 years. Many provinces like Yorkshire, Derbyshire, and Essex etc has used this concrete surfacing.

A reduction in noise of 3 dBA is observed in UK which is equivalent to reduction of traffic flow almost to half. With times several noise reduction options are developed but whisper concrete serves good for many years and still they are serving purposes. Now-a-days with the development of polymer science, polymer modified concrete or asphalt pavements are conducting test for best performance of highway pavement surface. Dear reader we will publish posts regarding polymer modified concrete pavement in upcoming post. Please stay with us.

How are Curled Slab Foundations Repaired?

Here we will discuss a method for repairing/raising settled portion of slab-on-grade foundation. We are concerned with the repair work where slab foundation repair must not interrupt services of a floor. We are not going to conventional slabjacking process. So a quick process of repairing is required where equipment, after repair, can be packed quickly and little cleaning work is required. This can only be done by using polyurethane foam stabilizer.

At first we will learn the phenomenon slab curling. This is nothing but a form of slab distortion in a curled shape. Normally distortion is observed near edges and curled shape is formed. It brings an unaesthetic and unserviceable floor slab. If it is not repaired the distortion reaches to extremity and requires through repair as under heavy vehicular load, it may distressed completely.

As mentioned earlier, conventional methods are not used in busy floor slab to avoid space loss during construction, interrupting regular service of floor. In industrial floor it is essential to keep operating both repair and business operation.

Our aim is to fill cavities below the curled slab. Only a special grout injection, penetrating the slab and filling can serve the both purposes and only polyjacking can do this. It need only small injection holes and hardened within short time. In case of slabs that is sunk severely a pressurized injection is often adopted. This injection is applied in routine to optimize the time and these are made complying production and business schedule.

Dear reader to learn much about polyjacking we have to wait for next post and there we will learn about the scope of polyjacking and relative comparisons with traditional slabjacking will also be provided with the mechanism involved in polyjacking.

Noise Reduction in Concrete Pavement in California

Dear reader so far we learned about exposed aggregate surface finishing for reducing noise from concrete pavement while vehicular traffic move over this pavement. This also provides skid resistance that are reduced by wearing action of tyre treads. This surfacing becomes popular in Belgium, Austria, United Kingdom and many other countries of that continent. We will learn here another method of noise reduction instead of providing any overlay over worn out concrete surface.

There is a special grooving technology named concrete grinding and grooving method. This method has been successfully used in United States for many years. Especially in California this method of grooving were provided in many roads and highways. Now we will learn how this technology is applied.

In the middle of 1960 diamond grinding became feasible as large scale technology in California for restoration of concrete pavement

In this method a plant that is equipped with saw blades is used. The blades have diamond tip and spaced closely. That provides grooving texture to the concrete pavement. This process of surface restoration is very economical too. This method requires only half of the cost involved in overlaying asphalt over concrete.

The section where this method is used, it is found that the treated surface have an improvement of 54% in skid resistance. This method renders a noise reduction of (4-6) dBA in a vehicular traffic moving speed of 50 mph. In a greater vehicular speed this reduction in noise is found even better. In the next post we will discuss another method of noise reduction in concrete pavement known as CRCP. Please stay till then with us.

What should be Working Stress of Concrete in Designing Pile Foundation?

Dear reader after long time, we are publishing back to foundation engineering. This post must worth be a part of foundation engineering but there have also some content on concrete engineering too. Dear reader so far you have realized that we are answering such questions which are known to all but not easy to understand or express. Now we are solving a question that is regarding working stress on pile or more precisely on single pile.

Do we know what working stress is? No we will not answer this question here. So come to the point –limiting working stress in different piles. Here different piles means materials that comprise a pile may be concrete, steel or timber piles. At first we will know about concrete piles.

The working stress must not exceed (0.25-.033) X f’c in cast-in-situ concrete piles. Where f’c means compressive strength of unconfined concrete test cylinders after curing properly through 28 days.

Now we are providing information for steel piles. Working stress, in case of steel piles, at the tips is generally limited to 12.6 Ksi.

We can explain to some extent in regarding concrete piles. For steel pile you have to wait. But for your kind information, we have published some post regarding steel piles. Of these, splices of steel piles and corrosion problems of steel piles become popular. You are invited to all those posts, especially these two. Now, earlier, we have provided a range of limit of working stress in concrete piles. The lower limit of range is for piles where placement difficulties of concrete are considerable. This situation may occur where:

a. Small diameter of the tip of piles where size is decreased with depth.

b. Batter piles.

c. Heavily reinforced piles

d. Irregularities in side walls of shell

Proper allowance must be provided for prestress, in case of prestressed piles. Dear reader we have to finish this post here. In the next post we will discuss about point bearing piles. Keep tuned with the latest post, we will be answering your questions.

Application of Exposed Aggregate Concrete Surfacing in UK

We all know that concrete pavement is costly relatively to that constructed with bitumen. But sky high price increment of bitumen, raised question to highway engineers whether it is relevant to use such pavement considering its longevity and frequent maintenance requirements. Then concrete pavement is tested and initial costs of both materials are compared. Now these are almost same. Regarding longevity a bitumen surface may serve only 7-10 years whereas a concrete surface can serve successfully for 15-40 years.

With the longevity a slight modification in wearing course can render a concrete pavement of lower noise pollution. Yes we are talking about exposed aggregate concrete surfacing. We have learned about it in our previous few posts. We are providing here a link in regards to it.

Expose aggregate concrete surfacing is compressed to EACS in this post for convenience of writing this post. EACS has successfully applied in several UK roads and served as good for last 15-20 years. We are providing a list:

1. M18 in the Yorkshire

2. A50 in the Derbyshire

3. M23 near the Gatwick

4. A13 in the Essex

5. A449 in the Wales

We have already learned about how aggregate are exposed in EACS. Its exposed aggregate surface provides a random contact points with tyre treads and reduce noise pollution. It can reduce noise up to 3 dBA. Can you realize 3DBA noise reduction? It is almost equivalent to a 50% reduction in traffic flow. With noise reduction of this level it provides excellent skid resistance to the surface and requires low long term maintenance.

We will discuss about another method of noise reduction and providing skid resistance known as concrete grinding and grooving un the next post. This reduces noise more efficient than EACS.

What is the Basis of Purchase of Ready Mixed Concrete?

During ordering concrete in ready mixed form, it is important to know the basis of purchase. As concrete is a costly materials, purchaser should know how he could receive accurate and quality concrete with right quantity. Now we will learn basis of purchase of ready mixed concrete in this post.

In one word, we can say the basis is cubic meter or cubic yard of concrete. The concrete must be in unhardened, freshly mixed, discharged from the mixer or other hauler system. Now we will explain what should do to measure volume. We have to know how to determine the volume for which the manufacturer provides bills to purchaser.

Now question is how mass of particular batch can be calculated. This is simple.

Mass of particular batch = While enter in batch {(summation of masses of all   

                                       materials) + (mass of water)}

                                                or 

                                          Delivered mass of net concrete from batch

ASTM test method C138 provides test procedure for determining concrete mass for volume unit. In this method, a container of 14 cubic liters (1/2 cubic feet) is used for sampling. The result is taken as an average of three samples at least. ASTM practice C172 provides procedure to collect sample from truck load. Each sample (out of three) is recommended to take from midpoint of respective truck load.

Dear reader notice that we have said unhardened concrete is used to measure the purchase volume. The volume of hardened concrete is found often lesser than that of unhardened fresh concrete. Spillage, wastage, spreading of not well stiffened formwork, loss of entrained air voids and in case of foundation concreting or concreting over ground-over excavation causes loss of volume of hardened concrete.

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.