What is Finishing of Concrete?

Through finishing process, concrete becomes ready for service. This is the last step of production of concrete following by mixing, transporting, placing, compaction and curing process. Concrete is the material that need utmost are in every operations stated above. We have discussed about all process except finishing. In this post we will have an overall idea about finishing.

Actually finishing does not require for every concreting operation say in case of casting concrete for beam we do not need finishing. But in case of concreting for abrasion exposure we need finishing of utmost quality like runway, taxiway, road pavement, flooring for industrial operation, container terminal and so on. Even in residential purpose flooring concrete requires quality finishing. Concrete is sometimes termed as drab material of ugly finishing having no way to establish architectural appearance.

Now-a-days engineers bring artness to concrete applying different finishing techniques. Prefabricated panels of concrete either for wall or slab, even for roofing are used successfully, having excellent finishing and esthetic effects. Recent development of surface treatment provides much flexibility in finishing of concrete. Now we can produce textured concrete of having finishing like board marks, many types of lining can be provided with special techniques. These developments of finishing replace the costly veneering to hide concrete.

Surface finishing can be classified as

a. Formwork finishing

b. Surface treatment

c. Applied finishing

In the very next post we will discuss applied finishing followed by other two.

What is Parametric Study in Mat Foundation Analysis?

In the last posts about mat foundation, we have discussed many parameters that are used in analysis and design of mat foundation. Say these parameters are:

a. Es=modulus of elasticity of soil

b. µ =Poisson’s ratio

c. Ks=q/δ=Modulus of subgrade reaction in vertical direction

Many parameters with this parameters cannot be predicted accurately as their have many difficulties. To account this problem, geotechnical engineers and structural engineers together perform a study called parametric study.

In this parametric study engineers vary the values that are used in foundation design. There have a range of variation. This is

(1/2 X furnished value) to (10Xfurnished value)

With this wide range of variations in parameters, the geotechnical engineers carefully review the results through the whole design process.

When engineers are not satisfied with solutions, then it is assumed appropriate adjustments are done in development concept. Now we will know what the adjustments are. The adjustments are:

1. Reduction in weight of structure

2. Enlarging mat foundation area

3. Reducing net pressure changing mat base area

It should keep in mind that, the adjustments should take in presence of both structural and geotechnical engineers.

Performance of Bituminous Compounds as Concrete Curing Membrane

At first we will learn why membrane curing for concrete is required. This is due to deficiency of water i.e. the region where water shortage is acute, membrane curing is adopted. In case of concreting in inaccessible and difficult to reach regions, supervision after concreting with qualified supervisor or engineers is not possible. 

In this region the workmanship of local worker is also low and sometimes they have no idea about importance of curing-leaving no way to depend on them and membrane curing is adopted. The further discussion on different aspects of membrane curing will be published in upcoming posts-keep tuned.

Bituminous compounds are used to form a impervious film over concrete surface to prevent loss of moisture due to evaporation. But there have a limitation of using bituminous compounds as moisture barrier. This is it absorbs heat from environment being black in color. This causes increase in temperature of the concrete. We all know hydration of concrete depends not only on moisture loss but also depends on ambient temperature. This limitation is overcome by applying a bright color coating on bituminous compounds. For economy this white coating is done by lime wash.

Bituminous compounds sometimes are used in the interface of concrete and ground to detach both from come in contact as adsorption of water from concrete to ground can also hinder hydration process.

How does Calcium Based Treatment Improve the Properties of Black Cotton Soil?

Lime treatment of expansive soil like black cotton soil together with fly-ash and cement is known as calcium based treatment. The aim of this treatment is to alter clay mineralogy to have a better founding soil without significant swelling followed by shrinkage. This process of treatment results chemical reaction of exchanging ions of particles of clay mineral with positive species of ions. This process is called “cation-exchange” reaction.

Through the process of flocculation-agglomeration, this treatment clump tiny clay particles to form a larger particle. This process includes the reaction of positive charged particles with particles having negative charge.

Calcium based treatment also left cementing agent in the black cotton soil mass to form a soil mass of altered properties. The resulting effect of calcium based treated soil is a soil of reduced swelling and shrinkage potentials having better strength properties. In case of highway construction works this method is widely used. 

Octahedral sheet is sandwiched between two tetrahedral sheets to create the mineral structure of Black Cotton soil

In India black cotton soils are found in over wide range of area. Highway construction works in most cases face this problem and the calcium based treatment is adopted. The Molecular Sandwich of Black Cotton Soil is discussed in previous post. Better understanding you can read this.

What is Liquid soil Stabilizer for black Cotton Soil?

We have discussed earlier about lime stabilization for black cotton soil. Lime stabilization is the oldest treatment method for expansive soil, whatever the expansive soil, black cotton soil, regur or vertisol. Now we have to know about efficiency of this treatment.

Whenever the efficiency of lime treatment is concerned, It can be concluded that expansive soil having high sulfate content do not respond good. This condition may occur many region of the world.

In building construction process it can sometimes relocate the structure considering geotechnical and geological conditions. But in case of highway construction, in most cases there have no alternative to realign the course of highway. As realign of highway course can deprive a locality form transport facility where overlain expansive soils are exist through whole area. So highway department of India, United States or many countries of the world are very much worried about that and credits of major developments in this stabilization process mostly go to highway engineering researchers.

Now we learn about liquid soil stabilizer-

Now-a-days numbers of modern stabilizing products are offering by different manufacturer to alter disturbing properties of black cotton soil. These stabilizers is called liquid soil stabilizer. Here we are providing a list of those products:

a. Polymer treatment-this treatment process utilize both inorganic and organic polymers

b. Very interesting, Enzyme treatment-this treatment process utilize organic catalyst of various forms.

c. Cation exchange treatment.

As everyday many highway and building foundations are affected by black cotton soil, foundation engineers need new effective and efficient stabilizing products. Bur the products stated above are still require more research and foundation engineers should use this products verifying the experimental performance of this products.

What Should be the Suitable Height of Concrete Layer?

Many aspects of compaction and specially compaction by vibration of concrete have already discussed in previous posts. Vibrators have capacity to compact to certain depth below concrete layer. Depending on the type of vibrator the capacity of vibrator may vary. But there have standard practice to provide layer height of concrete to have a dense concrete having no air void without segregation. We will now know the usual practice of placing height of concrete layer.

It should keep in mind that the depth of layer depends on placement method and method and type of compaction. If hand compaction is used, the depth of concrete layer definitely much layer than that for machine vibration.

Here we are discussing about height of concrete layer that are compacted by vibrator. Generally concrete is placed at a thickness of less than 600 mm. But the thickness of initial placement of concrete should be less than 150 mm. When height of concrete layer increased, it helps performance of vibrator with increased super imposed load. But excess height results a way of entrapping air in concrete. Vibration of too deep concrete layer, results trapping air to come up by vibration. In some special cases like dam, heavy pile cap etc. sometimes the depth may be greater than 1 m but these heavy concreting works require powerful vibrator of adequate capacity. So too deep layer (greater than 600 mm) are avoided in normal practice.

Structural Slab: A Slab on Grade Foundation Repair Option

The most common problem that expansive soil can result in slab on grade foundation is expansion pressure exerted to slab and resulting impacts of this expansion pressure are discussed in many posts of this blog. Here we will try to find solution for such problem. 

Structural slabs are provided with extra thickness and with the addition of steel reinforcement, it resists expansion pressure. In this process of foundation repair, the existing concrete slab are dismantled and structural slab are provided with reinforcement spacing generally satisfying shrinkage and temperature requirement of reinforced concrete through both directions.

Some may have seen application of dowels. This situation arises when existing load bearing foundation cannot be removed. To achieve this purpose, existing thin slab just above the load bearing foundation are isolated by cutting remaining slab by concrete saw. The reinforcement from new structural slab is doweled to the existing slab.

Required holes are drilled in the vertical face of existing slab and epoxy-glued rebar are passed through the hole. The size and depth of hole are specified by the manufacturer depending on size of bar.

It is usual to remove existing soil and replacing it with non-expansive soil for both new construction of foundation on expansive soil and repair work of slab on grade foundation. But sometimes structural slab provides an economical and safer solution than replacing existing expansive soil with non-expansive one.

How is Vibrator Applied to Reinforced Concrete Member?

We have learned about different compaction process of concrete in previous posts. In the recent post we have discussed about over vibration of concrete. Now in this post we will learn how vibration is applied to reinforced concrete member. 


There have many difficulties in vibrating congested reinforced concrete member especially near beam and column joints or in heavily reinforced mat to column joints in column strips. These situations become worse when basement wall passes through the columns. To have compacted dense concrete having no air void in reinforced concrete member the reinforcement detailing require special attention.

The detailing should have such provision that vibrating head passes through the reinforcement. The spacing of bars should be detailed properly. Reinforcement can be grouped to have more space to permit vibrator pass through the gap freely. But the grouping width must be less than 25 cm and a spacing of 7.5 cm has to be provided between two groups. In individual group the bar spacing can be reduced up to 2/3 of nominal coarse aggregate size.

In case of closely spaced reinforcement, special care is provided to vibrate the concrete to avoid pockets or accumulation of grout. In case of properly tied and fastened reinforcement arrangement or where some portion of concrete in the member has already stiffened i.e. set vibrator can be pressed against reinforcement. But if this done to improperly supported and tied reinforced member, the formwork and internal arrangement of reinforcement may collapse.

What are the Responses of Calcium Treated Black Cotton Soil?

In the previous post we have discussed many topics about properties of black cotton soil and foundation considerations of these type of soils. Some of these become popular to reader as they have several thousands of viewers in a month. This is a great achievement to us. You can read all these posts by following the link “black cotton soil”. In some posts we have provided some reinforcing methods for black cotton soils. Now in this post we will learn about a form of chemical treatment with calcium. To have better understanding you can first read “Molecular Sandwich of Black Cotton Soil”.

Chemical treatment is used to change the mineral structure of clay and thus reduction in its expansion potential. For this purpose calcium oxide treatment is the oldest method to treat black cotton soil. Calcium oxide is nothing but lime and with the presence of water it changes the properties of black cotton soil.

Here we are trying to list the actions that are taken by lime and subsequent response of black cotton soil against these actions-

a. Lime produce a cation exchange reaction where ions are exchanged

b. In the solution the atoms with positive charge are substituted to opposite form of ions of crystal of clay minerals.

c. Smaller clay particles becomes large one by flocculation-agglomeration process

d. Mineral structure changed by the reaction of particles having positive ions with negative one.

e. Cementing agents are formed in expansive soil

f. With the above alteration of soil properties the swelling and shrinkage potential get minimized to some extent not to generate any foundation problems.

Thus the resulting treated black cotton soil becomes a strong, firm and less expandable good grounding bed for placing foundation.

How is Porosity Arisen Due to Excess Water in Concrete Mix?

Concrete mass is expected to be dense and heavy material. Concrete is a solid mass that are formed by bonding action of hydrated cement with aggregates in presence of water. The water is the component that makes concrete porous with the other facts. Here we will learn how water makes concrete porous.

During chemical reaction, named hydration, the concrete becomes mass like rock. In the chemical reaction the amount of water is very important. The amount of water is determined by the amount of cement used in mix proportioning. 

To avoid many difficulties in mixing, placing and to facilitate compaction process in many critical placing conditions concrete are made workable by adding water in excess of that required for binding chemical reaction.

If with this excess water in concrete mix, it is placed and subsequently finished, the excess water try to come out from the mix and it succeeded in many ways. Most of excess water comes out through bleeding and rest moisture is removed from concrete by evaporation. This process leaves a concrete mass of having capillaries or small voids. The resulting concrete becomes a porous mass of low durability properties. Through this finished product vapor molecules and microscopic liquid have easy excess and the results are many impacts of deterioration of concrete and reinforcement embedded within it.

How is Water Added to Concrete Mix in Mixing Process?

We all know the amount of water is very important to have perfect hydration of cement and water/cement ratio is one of the most important factors to control strength of concrete without influencing economy of mix. So the amount of water added to mix should be accurate and no loss of water is expected to have sound concrete mix.

Graduate bucket is the way in which water is added to concrete in liters. But now-a-days use of graduate bucket is becoming limited as it has possibility to water spillage. Now either vertical tank or horizontal tank is used to measure water. After each batch they are filled up. With this facilities water addition can be controlled to any desire quantities. In many cases, water supply includes water meters. With the help of water meter exact amount of water can be supplied to mixer. 

The latest batching plants have microprocessor controlled sophisticated automatic arrangements to weigh batching. This provides not only exact amount of every constituents of concrete but also provides desire moisture content in aggregate. Sensitive sensor automatically measure moisture content and whenever it find inaccurate moisture content it takes corrective measures to deduct water in excess of desire amount. In many countries of the world this modern batching plants are working for last decade.

How to Determine Over Vibration of Concrete in Compaction Process?

Vibration is a mechanical process to achieve well compacted concrete. During compaction process, it is the main concern for supervisor or vibrator operator is to provide through vibration to concrete mix without segregation. In a well proportioned too or not too much vibration does not hamper the placing process of concrete. But in case of concrete having gap graded aggregate having large quantity of mortar than void in relatively large coarse aggregate i.e. not well proportioned or where due to reinforcement congestion or for any other unexpected condition high workability of concrete is required, over vibration results segregation.

This process produces accumulation of lighter constituents to the surface of concrete. The way how over vibration can be diagnosed are listed below:

a. Mortar comes out through the faulty joints in forms after application of vibration. 

b. Coarse aggregate are found settled beneath finished surface.

c. Laitance on the surface.

d. Numerous air bubbles are appeared on the surface.

e. Foamy appearance of concrete.

An experience supervisor or vibrator operator can easily determine the over vibration with the above mentioned physical appearance of concrete.

Revolution of Mat Foundation Analysis with the Development of Electronic Foundation Solution

Flexural rigidity of mat and soil modulus of subgrade reactions are not common term to foundation engineers who are analyzing and designing a mat foundation with the rigid beam method as discussed in earlier posts. They are used to assume the infinite rigidity of mat foundation and above two terms are totally ignored. This assumption leads to a unrealistic modeling of mat foundation as discussed before.

Conventional methods were/are used as they are simple and complexity in elastic analysis like finite element method cannot be solved easily as computing device are not available to foundation engineers. Now-a-days due to revolution of electronic calculation method using computer programming numerous types of input of parameters and their resulting solution can be predicted within minutes(like solution of any degree of matrix can be solved within few seconds). The advanced silicon chip technology provides computer extensive capability to solve laborious calculations and new advancement of these technology make such devices cheaper than ever.

Thus chances of errors and limitation of input many parameters are removed and solution like finite element method can solved easily.

We emphasize on the finite element method as it is the finest way to analyze mat foundation. In this method soil beneath mat is considered as elastic continuum and the mat itself as a plate. The finite element method of mat analysis can be solved conveniently with software “SAFE”. Friends keep an eye on the next posts to have an idea about SAFE to solve mat.

What are the Secondary effects of Retarder of Concrete Other Than Retarding?

We all know the general constituents of concrete. Other than aggregate, water and important cement, some materials, called admixtures are added during or before mixing of concrete to change its properties like setting time, workability, water proofing and many other properties. In this post we will discuss retarding admixtures. From the name we can easily realize that it retards concrete to set early.

It is interesting to know that some retarders in most cases reduce the water requirements of concrete mix. So the retarders are frequently termed as water reducing retarder. According to ASTM C494 retarders are type B chemical admixture but they also found in type D which deals both with water reducing and retarding chemical admixture.

The secondary effect of retarder is it produces a concrete mix of low W/C ratio requirement having desire workability and result a concrete mass of better strength for a particular cement content. These concrete also becomes less permeable rendering a durable structure. In addition some retarders produce sufficient air bubble to act as air-entraining agents for concrete mixtures. Thus the performances of retarder are manifold including:

a. Better workability

b. Higher strength

c. Better durability

As an example, Lignosulfonate retarder has influence in the early development of strength with its main purpose of retarding. The cement slurry containing lignosulfonate retarder is successfully used in oil industry with the above extra advantages.

What is Impact of Over Vibration of Concrete Mix?

During mixing process of concrete air get entrapped into the concrete mix. This entrapping process also happened during transporting and placing of concrete. Here in this post we will discuss about over compaction of concrete using mechanical compactor widely known as vibrator. There have different types of vibrator. We will discuss the vibration impact in general irrespective of types of vibrator.

At first we will learn what is the purpose of using vibrator?

This is simple vibrators are used to remove entrapped air from concrete mix completely. Now come to the point over vibration. We are not concerned with the well proportioned and designed concrete mix. As such mix with normal weight aggregate generally do not require extended vibration and if extended vibration is undertaken it will not produce any harm to concrete mix. But for many conditions of placing concrete sometimes workability of the mix are expected to be high. Over vibration to such concrete mix is harmful. Here a list of conditions where over vibration are concerned are provided:

A. Mortar quantity is much more than voids present in coarse aggregate.

B. Unexpected grading of aggregate

C. Too workable mix

The harm that over vibration does is segregation. These exceeding vibration results:

A. The smaller and lighter constituents of concrete mix come out to the surface.

B. Laitance phenomenon is observed on the surface.

C. Mortar is observed to leak through the formworks where they found defects in joints.

D. Poor abrasive resistance of concrete

E. Sometimes a weaken plane in concrete is observed

F. The concrete becomes weak against exterior agents of concrete deterioration like frost etc.

What is the Thickness-Settlement Relationship of Mat or Raft Foundation?

When a differential settlement of greater degree is suspected for shallow foundation, raft or mat foundations are used. In case of soil having loose and soft soil pockets, the mat foundations are adopted to minimize differential settlement. Mat foundation generally covers area equal to base area of structure or greater and it continues in both directions.

Foundation engineers often change the thickness of mat foundation to provide economical solution of costly mat foundation and from analysis it is found that the thickened portion of mat should be provided below columns. One observation shows that mat thickness can be reduced up to 40% away from respective column faces. But this thickening required careful observation considering all other factors geotechnical as well as stresses that can be concentrated at sensitive locations.

Though thickening of mat render a greater bending moment capacity, it provides greater punching shear as well beam shear capacity to the mat. Hence a uncracked section is achieved. But when economy is concerned, the foundation engineers pay attention to thickening in right location where stress concentration is much more resulting a overall thin but localized thick, economical mat foundation. Here in this post we will try to learn the settlement-thickness relationship.

It is found that greater mat thickness produce positive bending moments whereas it simultaneously produces a less negative bending moment. The maximum settlement of a structure founded with mat foundation is not influenced greatly by the mat thickness but it provides a significant reduction in differential settlement

What are the Analysis Methods for Raft Foundation?

In the previous post we have learned about rigid beam method for raft foundation analysis. In this post we will learn overall idea of all methods of analysis. The methods that are available to analyze a raft foundation are:

a. Rigid beam methods

b. Elastic or non-rigid method

In rigid beam method of analysis as discussed in early posts is a simple static method. There have some assumptions that make this method less appropriate for analyzing rafts. We will not discuss much about this method. We will have only summary of these method. In this method mat is considered as true rigid body which is the main limitation and this method is not supposed to model mat as in actual condition. With this limitation this method was used through the decades as it is simple and more refined method of modeling mat to represent actual situation was not available.

Now with the help of electric calculation we can model mat nearly actual condition and this method is elastic or non rigid method. In this post we will learn only overall idea of non-rigid method of mat analysis.

Non-rigid method involves followings:

a. Using elastic theory-ready made closed formed solutions

b. Method of discrete element, dividing mat into some elements along grids

c. Beams or plates in elastic foundations

d. Beams or plates in elastic continuum 

Of these, the method of discrete element includes:

1. Finite difference(FDM) method

2. Finite grid(FGM) method

3. Finite element(FEM)method

Of these, finite element method of analysis is the finest way to model and analyze mat. In this method mat are assumed as plate supporting on elastic foundation.

Thickness-Rigidity Relationship of Mat or Raft Foundation

In the previous post we tried to find answer of different query about mat foundation. Here we will try to make relation between mat thickness and its rigidity. In normal condition an uniformly thickened mat foundations are common. But foundation engineer may change thickness to have economy of construction.

The thickened portion of mat is located below columns as it provides maximum economy. Case studies of many mat foundations show that a reduction in thickness of 40% can be allowed away from individual column faces. 

But in this purpose with variable thickness and applying all factors, its effects on mat rigidity have to be investigated carefully. Though the impacts of thickness were found little on maximum settlement or load sharing, it affects bending moments and differential settlement. The thickening of raft up to certain limit renders a greater bending capacity. But above 1.5m thickness a little effect on maximum bending capacity are observed.

It is found that negative bending moment is reduced with increment of raft thickness whereas it simultaneously produces a increased positive bending moment.

What is Modulus of Subgrade Reaction in Foundation Engineering?

At first we will provide an idea about subgrade reaction. Subgrade reactions is the pressure distribution that is developed due to reaction of a subgrade. The reaction is developed due to loads that are imposed to foundation structure. The determination of the modulus of subgrade reaction is a complex attempt as it depends on many parameters of individual types and density of soils.

In this blog we are trying to describe the easiest way to determine civil engineering parameters. Here we will provide an set of empirical equations which depends on undrained shear strength for clay and standard penetration test for sand. This is worth mentioning that empirical equations are fairly good but we have to know where should they be used?

The equations below can be used when data to determine modulus of subgrade reaction are not available i.e. in case of unpredictable soil conditions: 

where  s_u=shear strength in undrained condition(t/m²)

N_SPT  =Standard Penetration Test(SPT)value

We will discuss elaborately about modulus of subgrade reaction in next posts as this very important value that is used in designing foundations. Now-a-days electronic solution of mat foundation are done using digital computer where mat foundation modeling having discrete elements are performed with this important parameter of moduli of subgrade reaction.