What is Ductal?

Few Years back in 2006; researchers at Iowa State University have developed a new type of concrete that is much stronger than conventional concrete. It can withstand pressures up to 595,000 pounds — more than the weight of seven semi trucks.

A new kind of concrete called Ductal that might allow bridges to hold more weight and last longer. Although it is 10 times more expensive than traditional materials but stronger and virtually impermeable, helping bridges become more durable.

The researchers conducted a load-bearing capacity test using a 71-foot beam made out the new concrete. They applied increasing amounts of hydraulic pressure to the top of the beam to see how much it could withstand before breaking. It finally broke with a loud pop at 595,000 pounds. The ultra-high performance concrete is made from sand, cement, water and small steel fibers. Standard concrete uses coarser materials. The new concrete is specifically engineered to include finer materials and steel fibers, making it denser and stronger.

We are extremely thankful to Dr. Varenyam Achal for sharing  this research on our site and thus helping civil engineering students.

It’s safe to say that without microbes, biotechnology would be an extremely limited science. Microbes are microscopic organisms such as fungi (which include yeasts), bacteria and viruses. They not only provide the foundation for much of the basic research involved in biotechnology, they help to create durable building materials and structures.

The early scientific study of microbes concentrated on their effects, such as causing disease. Eventually, scientists discovered microbes could be used for the study of processes which are common to all living organisms. An innovative alternative approach lies in the combined use of microorganisms, nutrients and biological processes naturally present in the subsurface soils to effectively improve their engineering properties. Considerable research on carbonate precipitation by bacteria has been performed using ureolytic bacteria. These bacteria are able to influence the precipitation of calcium carbonate by the production of an enzyme, urease (urea amidohydrolase, EC 3.5.1.5). Calcium carbonate precipitation occurs as a consequence of bacterial metabolic activity that raises the pH of the proximal environment.

Recently I discovered and improved few bacterial species which were able to precipitate calcite at higher rate and eventually this process lead to improved compressive strength, reduced permeability and low corrosion rate of reinforcement.

Biocement, a self-healing material to enhance durability of building structures and conservation of cultural heritages

Although hundreds of thousands of successful concrete and buildings are annually constructed worldwide, there are large numbers of concrete structures (including historical monuments) that deteriorate or become unsafe due to changes in loading, changes in use or changes in configuration. The constant developments in the field of civil engineering and the growth of industrial activity have created a growing demand for materials for the construction industry that do more and more to comply with structural requirements and meet stricter demands for working conditions and environment. Traditionally, mechanical strength has been the main criterion used when choosing building materials such as cement, concrete or bricks. Compressive strength, permeability and corrosion analysis are the most common used measures in designing of buildings structures. Considerable effort has been devoted to develop high-strength materials. However, with increasing volumes of constricted facilities that need to be maintained the focus is shifting towards durability.

Besides building materials preservation of the cultural heritage, socioeconomic growth and sustainable development is finding considerable resonance amongst specialists in the field. It calls for an innovative strategy for the maintenance of our cultural heritage. This strategy implies that the protection of historical buildings represents an important prerequisite for peace and stability and provides social and economic opportunities at the same time. The preservation of culture contributes to the identity of the citizens, creates jobs, supports the economy and promotes the responsible handling of societal resources. Although there is a great deal of knowledge and information on world heritage monuments, this is lacking in respect of standard monuments both at national level and international level. There is a need for research at this level into the number and quality of monuments and historical sites. Large sums of money are being spent worldwide on measures for the preservation of monuments and historical buildings. The economic and ecological commitment to the preservation of monuments and historical buildings requires, however, a prudent handling of the appropriate funds. This demands an optimization of damage analysis procedures and damage process controls as well as the development of monitoring and early warning systems for damage prevention. Therefore, the goal needs to be the implementation of permanent preservation measures, which requires long-term maintenance.

All building materials are porous. This porosity of building material along with ingress of moisture and other harmful chemicals such as acids, chlorides and sulfates affect the material and seriously reduce their strength and life. An additive that seals the pores and cracks and thus reduces the permeability of the structure would immensely improve its life. Conventionally, a variety of sealing agents such as latex emulsions and epoxies etc.; and surface treatments with water repellents such as silanes or siloxanes are used to enhance the durability of the concrete structures. However, they suffer from serious limitations of incompatible interfaces, susceptibility to ultraviolet radiations, unstable molecular structure and high cost. They also emanate toxic gases.
In order to overcome the shortcomings of conventional sealing agents, materials with self-healing capability can be used effectively. Use of urease producing microbes addresses these problems effectively, as these continue to survive and grow within the concrete structure after the initial use. Urease helps in mineralization of calcium carbonate, by hydrolyzing urea present in the environment. It releases carbon dioxide from urea that combines with calcium ions resulting in deposition of calcium carbonate in the form of calcite. Due to urease activity, bacteria are able to use urea as a sole nitrogen source and produce ammonia, which increases the pH in the proximal environment, causing Ca2+ and CO32- to precipitate as CaCO3. These unique properties make it particularly suitable for many applications in civil engineering (concrete structures, plasters, mortars, prefabricated elements, refractory elements, bricks, natural stones, etc.)

A microbial additive that helps in calcite precipitation with urease would enhance durability of building materials as well preserve the cultural heritage.

I am pleased to present herewith my preliminary findings of the effects of microbial additives (where I used Sporosarcina pasteurii, previously known as Bacillus pasteurii, a facultative anaerobic Gram-positive soil bacterium) to enhance the durability of building materials. The significant amount of data, some of which are attached hereto, accumulated to date leads us to the preliminary findings:

1. Microbial additive resulted in improvement in compressive strength of mortar by up to 38%.

2.Microbial additive can remediate cracks in building materials and monumental stones and regain strength within 28 days.

3. To make the process economic, microbial additive can be prepared by growing cells using industrial by products such as lactose mother liquor, corn steep liquor as nutrient sources.

4.Microbial additive can enhance the durability of bricks by reducing their permeability and increasing compressive strength.

5.The reduced permeability rates resulting from the microbial additive will increase the concrete structures’ useful life.

The data accumulated to date are, in my opinion, sufficient in quantity and trend to allow me to draw some preliminary conclusions with a reasonable confidence that in future it will further support the preliminary findings. As previously stated though the study period has not yet run the full course, the data and trends indicate the microbial additive is having the beneficial effect of enhancing the durability of building materials and preservation of cultural heritage.

We are extremely thankful to Varenyam Achal for publishing these research finding on our site and thus helping people who are interested to explore this unknown field.

Name: Varenyam Achal
Mailing Address: TIFAC-CORE in Biotechnology, Thapar University, Patiala-147004, Punjab (India)

A long time used material in concrete is for the first time fully replaced by a nano material.It is well known in physics and chemistry that a well designed and developed nano material produces better and cheaper cost results than traditional materials, thanks to the stabilization and reinforcement of matter properties at this level: a thousand fold smaller than the older level: “micro” (0.000001 mt).

Micro silica has been one of the world’s most widely used products for concrete for over eighty years. Its properties allowed high compressive strength concretes; water and chemical resistant concretes, and they have been part of many concrete buildings that we see nowadays. Its disadvantage, though, has been its relatively high cost and contamination, which affects the environment and the operators’ health. As micro silica, as a powder, is thousand fold thinner than cigarette smoke. Operators must take special precautions to avoid inhaling micro silica and not to acquire silicosis, an irreversible disease.

In the middle of 2003, a product which could replace micro silica seen the contaminant effects, having the same or better characteristics and at a reasonable cost was on the design table. The goal: silica fulfilling the environ-mental regulation: ISO-14001.

Using tools from physics, chemistry and recent nanotechnology advances, the challenge was fulfilled.Lab tests and production tests proved that the nano silica did not contaminate (because its state), but it also produced better results than micro silica, and a litre bottle of the product was equivalent to a barrel full of micro silica, extra cement and super plasticizing additives.

Because of its innovation the nano silica was tested for over a year in the world’s largest subterranean copper mine to prove its long term characteristics. Cuore concrete takes care of the environment, the concrete and the operators´ health. It is the first nano product that replaced the micro silica.Cuore concrete surpassed the expectations of its design and gave concrete not only the high initial and final resistance but in addition, plasticity, impermeability, minor final cost of work, and cement savings of up to 40%. Also, it lowered the levels of environmental contamination.

In addition, a liter bottle of Cuore concrete equals a whole barrel of micro silica, extra cement and super plasticizers. If before a 2 meters thick beam was required to hold a bridge correctly, now only 75 cm are required. If before 28 days were necessary in order to achieve compressive strengths of 80MPa, now only 1 day is required. The pre stressed beams that before required 3 days to be ready and needed to be cured with water and steam , now require only 1 day and they do not need water.

Moreover, Cuore concrete became one of the first indicators of the properties that the next commercial nano cements in the market will have: nano particles of silica turn into nano particles of cement (nano cement) in the chemical reactions that take place in the concoction of the concrete, Thanks to all these advantages, the entrance of nano silica Cuore concrete into the market modified the concept of what is possible and what is not in the concrete field.

Since 2004, the greatest copper underground mine of the world, has been using nano silica concrete and the use of the micro silica in this deposit has been prohibited.

Properties of concrete with Cuore concrete nanosilica

• In high compressive strengths concretes (H-70), Cuore concrete is 88% more efficient than micro silica, added to concrete and super plasticizers. ( For an average 9,43 Kg. of Cuore concrete Nanosilica, 73Kg. of all the others additives are used).

• The production cost of is drastically lower than using the traditional production method or formulas.

• It has an air inclusion of 0% to 1%

• The cone test shows that It preserves the cone shape for more than one hour. (with a relation of H2O/Cement=0.5, adding 0.5% of Nano silica of the metric volume of the cement used, it conserved a its circle shape of 60 cm for two hours, with a lost of only 5%). The nano silica has a plasticity that has been compared to the policarboxilate technology. Therefore the use of super plasticizing additives is unnecessary.

• High workability with reduced water/concrete levels, for example: 0,2.

• Easy homogenization. The reduction of mixing times allows concrete plants to increase their production

• Depending on the cement and the formulations used for concrete (tests from value H-30 to H-70), shows that the material provides compressive strengths between 15 MPa and 75 MPa at 1 day; 40 MPa and 90 MPa at 28 days and 48 MPa and 120 MPa at 120 days.

• Nano silica fully complies with ISO 14001 regulations regarding the environment and health. It preserves operators of the danger of being contaminated with silicosis and does not contaminate the environment.

It successfully passed all the tests and since the beginning of this year it is being commercialized in different parts of the world.

Immediate benefits for the user

1) Cessation of contamination caused by micro silica solid particles.

2) Lower cost per building site.

3) Concrete with high initial and final compressive and tensile strengths.

4) Concrete with good workability.

5) Cessation of super plasticizing utilization.

6) Cessation of silicosis risk.

7) High impermeability.

8 ) Reduction of cement using Cuore concrete Nanosilice

9) Cuore concrete nano sílica on itself produces nano cement.

10) During the moisturizing reaction of the cement, the silica produces CSH particles, the “glue” of the concrete ensuring the cohesion of all the particles.

11) Cuore concrete has a specific surface near to 1,000m2/gr (micro silica has only 20m2/gr) and a particle size of 5nm to 250 nm.

As a consequence of its size, Cuore concrete produces nano cristals of CSH, filling up all the micro pores and micro spaces which where left empty in traditional concrete production.
Former described function reinforces the concrete structure on levels, thousand times smaller then in the case of traditional concrete production. This allows the reduction of the cement used and gives the compression needed to reduce over 90 % of the additives used in the production of H-70 concrete.

Cuore concrete allows to save in between 35% and 50% of the used cement.We do stress that we recommend to change the formula of the concrete in order to take advantage of the characteristics of the Cuore concrete Nano silica particle.

Less material is needed to obtain better results, using Cuore concrete.

The results are the proof.

1) Resistance to compression from 40 to 90MPa in 1 day.

2) Resistance to compression from 70 a 100 MPa (or more) in 28 days.

3) Versatile: produces high resistance even with low addition (1 to 1,5 % of the cements weight) and gives self compacting characteristics with higher proportions (2,5 %).

4) Meets the norms of environmental protection (ISO14001).

5) 70% less use of additives as traditional silica, super plasticizers or traditional fibres.

6) Equal or minor raw material cost as in traditional ??production with super plasticizers, and or fibres.

This useful information is submitted to us by : Pascal Maes

Low Cost Housing is a new concept which deals with effective budgeting and following of techniques which help in reducing the cost construction through the use of locally available materials along with improved skills and technology without sacrificing the strength, performance and life of the structure.There is huge misconception that low cost housing is suitable for only sub standard works and they are constructed by utilizing cheap building materials of low quality.The fact is that Low cost housing is done by proper management of resources.Economy is also achieved by postponing finishing works or implementing them in phases.
Building Cost
The building construction cost can be divided into two parts namely:
Building material cost : 65 to 70 %
Labour cost : 65 to 70 %
Now in low cost housing, building material cost is less because we make use of the locally available materials and also the labour cost can be reduced by properly making the time schedule of our work. Cost of reduction is achieved by selection of more efficient material or by an improved design.

Areas from where cost can be reduced are:-

1) Reduce plinth area by using thinner wall concept.Ex.15 cms thick solid concrete block wall.

2) Use locally available material in an innovative form like soil cement blocks in place of burnt brick.

3) Use energy efficiency materials which consumes less energy like concrete block in place of burnt brick.

4) Use environmentally friendly materials which are substitute for conventional building components like use R.C.C. Door and window frames in place of wooden frames.

5) Preplan every component of a house and rationalize the design procedure for reducing the size of the component in the building.

6) By planning each and every component of a house the wastage of materials due to demolition of the unplanned component of the house can be avoided.

7) Each component of the house shall be checked whether if it’s necessary, if it is not necessary, then that component should not be used.

Cost reduction through adhoc methods

Foundation
Normally the foundation cost comes to about 10 to 15% of the total building and usually foundation depth of 3 to 4 ft. is adopted for single or double store building and also the concrete bed of 6″(15 Cms.) is used for the foundation which could be avoided.
It is recommended to adopt a foundation depth of 2 ft.(0.6m) for normal soil like gravely soil, red soils etc., and use the uncoursed rubble masonry with the bond stones and good packing. Similarly the foundation width is rationalized to 2 ft.(0.6m).To avoid cracks formation in foundation the masonry shall be thoroughly packed with cement mortar of 1:8 boulders and bond stones at regular intervals.
It is further suggested adopt arch foundation in ordinary soil for effecting reduction in construction cost up to 40%.This kind of foundation will help in bridging the loose pockets of soil which occurs along the foundation.
In the case black cotton and other soft soils it is recommend to use under ream pile foundation which saves about 20 to 25% in cost over the conventional method of construction.

Plinth
It is suggested to adopt 1 ft. height above ground level for the plinth and may be constructed with a cement mortar of 1:6. The plinth slab of 4 to 6″ which is normally adopted can be avoided and in its place brick on edge can be used for reducing the cost. By adopting this procedure the cost of plinth foundation can be reduced by about 35 to 50%.It is necessary to take precaution of providing impervious blanket like concrete slabs or stone slabs all round the building for enabling to reduce erosion of soil and thereby avoiding exposure of foundation surface and crack formation.

Walling
Wall thickness of 6 to 9″ is recommended for adoption in the construction of walls all-round the building and 41/2 ” for inside walls. It is suggested to use burnt bricks which are immersed in water for 24 hours and then shall be used for the walls

Rat – trap bond wall
It is a cavity wall construction with added advantage of thermal comfort and reduction in the quantity of bricks required for masonry work. By adopting this method of bonding of brick masonry compared to traditional English or Flemish bond masonry, it is possible to reduce in the material cost of bricks by 25% and about 10to 15% in the masonry cost. By adopting rat-trap bond method one can create aesthetically pleasing wall surface and plastering can be avoided.

Concrete block walling
In view of high energy consumption by burnt brick it is suggested to use concrete block (block hollow and solid) which consumes about only 1/3 of the energy of the burnt bricks in its production. By using concrete block masonry the wall thickness can be reduced from 20 cms to 15 Cms. Concrete block masonry saves mortar consumption, speedy construction of wall resulting in higher output of labour, plastering can be avoided thereby an overall saving of 10 to 25% can be achieved.

Soil cement block technology
It is an alternative method of construction of walls using soil cement blocks in place of burnt bricks masonry. It is an energy efficient method of construction where soil mixed with 5% and above cement and pressed in hand operated machine and cured well and then used in the masonry. This masonry doesn’t require plastering on both sides of the wall. The overall economy that could be achieved with the soil cement technology is about 15 to 20% compared to conventional method of construction.

Doors and windows
It is suggested not to use wood for doors and windows and in its place concrete or steel section frames shall be used for achieving saving in cost up to 30 to 40%.Similiarly for shutters commercially available block boards, fibre or wooden practical boards etc., shall be used for reducing the cost by about 25%.By adopting brick jelly work and precast components effective ventilation could be provided to the building and also the construction cost could be saved up to 50% over the window components.

Lintals and Chajjas
The traditional R.C.C. lintels which are costly can be replaced by brick arches for small spans and save construction cost up to 30 to 40% over the traditional method of construction. By adopting arches of different shapes a good architectural pleasing appearance can be given to the external wall surfaces of the brick masonry.

Roofing
Normally 5″(12.5 cms) thick R.C.C. slabs is used for roofing of residential buildings. By adopting rationally designed insitu construction practices like filler slab and precast elements the construction cost of roofing can be reduced by about 20 to 25%.

Filler slabs
They are normal RCC slabs where bottom half (tension) concrete portions are replaced by filler materials such as bricks, tiles, cellular concrete blocks, etc.These filler materials are so placed as not to compromise structural strength, result in replacing unwanted and nonfunctional tension concrete, thus resulting in economy. These are safe, sound and provide aesthetically pleasing pattern ceilings and also need no plaster.

For more on filler materials check Filler Materials Used in Concrete

Jack arch roof/floor
They are easy to construct, save on cement and steel, are more appropriate in hot climates. These can be constructed using compressed earth blocks also as alternative to bricks for further economy.

Ferrocement channel/shell unit
Provide an economic solution to RCC slab by providing 30 to 40% cost reduction on floor/roof unit over RCC slabs without compromising the strength. These being precast, construction is speedy, economical due to avoidance of shuttering and facilitate quality control.

Finishing Work
The cost of finishing items like sanitary, electricity, painting etc., varies depending upon the type and quality of products used in the building and its cost reduction is left to the individual choice and liking.

Conclusion
The above list of suggestion for reducing construction cost is of general nature and it varies depending upon the nature of the building to be constructed, budget of the owner, geographical location where the house is to be constructed, availability of the building material, good construction management practices etc. However it is necessary that good planning and design methods shall be adopted by utilizing the services of an experienced engineer or an architect for supervising the work, thereby achieving overall cost effectiveness to the extent of 25% in actual practice.

By Kelly Baldwin

Published in Construction Canada, v. 98, no. 1, Jan./Feb., 1998, pp. 28-29

Abstract: Conductive concrete is a cement-based composite that contains electronically conductive components to attain stable and relatively high conductivity. Potential applications include electrical heating for de-icing of parking garages, sidewalks, driveways, highway bridges, and airport runways, as well as electrical grounding.

Résumé: Le béton conducteur est un composite à base de ciment contenant une certaine quantité d’éléments qui assurent une conductivité électrique stable et relativement élevée. Les applications possibles sont : le chauffage électrique pour dégivrer les garages de stationnement, les trottoirs, les voies d’accès, les ponts routiers et les pistes d’aéroport, et la mise à la terre électrique.

Overview

Although concrete has existed in various forms over most of recorded history, it is a material that still has opportunities for exciting developments. Over a number of years, many unsuccessful research efforts were made to develop concrete that could combine good electrical conductivity with the excellent engineering properties of normal concrete mixes. The Institute for Research in Construction (IRC) has succeeded in achieving this challenging goal, with electrically conductive concrete (”conductive concrete” for short), a patented invention that offers future promise for use in a variety of construction applications.

Ongoing IRC research is now focused on optimizing conductive concrete formulations for the best combination of strength, electrical properties, and production methods at the lowest possible cost, leading ultimately to commercial development and widespread use.

Properties

Conductive concrete is a cement-based composite that contains a certain amount of electronically conductive components to attain stable and relatively high conductivity. In essence, the aggregates normally used in concrete can be largely replaced by a variety of carbon-based materials to achieve electrical conductivity in conductive concrete. This is achieved while retaining the desired engineering properties, as indicated in Table 1. The conductivity is usually several orders of magnitude higher than that of normal concrete. Normal concrete is effectively an insulator in the dry state, and has unstable and significantly greater resistivity characteristics than conductive concrete, even when wet.

 

 

Table 1. Conductive Concrete Properties

Electrical Resistivity (omega – cm)	1 – 40
Compressive Strength (MPa)	30 minimum
Flexural Strength (MPa)	5 – 15
Density (kg/m3)	1450 – 1850

Conductive concrete can be produced using conventional mixing techniques. The mixing process can be controlled, permitting design of mix formulations that are reliably repeatable, and achieve electrical resistivity values within the overall target design range.

Characteristics

While the engineering properties and mixing characteristics of conductive concrete and normal concrete are comparable, conductive concrete does have other distinctive characteristics beyond its ability to conduct electricity.

• The conductivity value is stable. The effects of moisture content, hydration time and temperature on conductivity are insignificant.
• It is lightweight: conventionally mixed, conductive concrete has a density of about 70 percent that of normal concrete.
• Conductive concrete is chemically compatible with normal concrete, bonding well with it if used as an overlay.
• Thermal stability is comparable to that of normal concrete.
• The colour of conductive concrete is a darker grey, reflecting its carbon content.

Applications

Conductive concrete has the potential to address a wide variety of applications, including grounding, heating, cathodic protection of reinforcing steel in concrete structures such as bridges and parking garages, and electromagnetic shielding. Several of these promising applications are described more fully below.

Electrical heating. Electrical heating using conductive concrete has excellent potential for domestic and outdoor environments, especially for de-icing of parking garages, sidewalks, driveways, highway bridges, and airport runways. This method of heating would eliminate or dramatically reduce the need for using salt, thus providing an effective and environmentally friendly alternative. Conductive concrete itself is the heating element, and thus is able to generate the heat more uniformly throughout the heated structure.

As part of the pre-commercial development process, an outdoor heated area 13 m X 3 m, roughly the size of a small driveway, was built with an embedded conductive concrete layer (Figure 1). The surface area has been kept continuously dry and free of snow over the course of most of an Ottawa winter, successfully melting over 3.5 m of total snow accumulation, and providing a scale proof of concept for conductive concrete de-icing applications.

The possibility also exists for using conductive concrete as an indoor radiant heat option. Both de-icing and radiant heating uses will require appropriate changes to the Canadian electrical code before commercial use in public areas becomes established.

Electrical grounding. Grounding is required for virtually every electrical installation. The main purpose of electrical grounding is to protect the equipment and occupants in the event of an electrical systems failure, or in special situations such as the presence of lightning or static electricity. The protection is achieved through a proper electrical connection between the systems usually by embedding an electrode underground.

The establishment of an effective, economical and durable electrical grounding system has always presented problems for the electrical engineer, but now many of them can be solved through use of conductive concrete. Conductive concrete grounding uses include creation of equipotential floors in such disparate applications as dairy barns, where small voltage differences can reduce production, through to electronics fabrication and handling areas, where the potential for costly damage to high-value semi-conductors and associated equipment caused by static charges can be high.

With its excellent structural engineering properties, conductive concrete is also a good candidate for grounding in a variety of utility uses. These include communications, and electrical transmission towers, as well as electrical transformer locations.

Commercial Development

IRC’s continuing research on conductive concrete and interest in licensing the use of this innovative new technology offers opportunities for progressive organizations to gain a competitive advantage in developing new products and improving existing ones in a variety of markets. IRC welcomes expressions of interest in the development of conductive concrete. For further information concerning conductive concrete, please contact Mr. Mark Arnott at 613-993-9811 (tel) /613-954-5984 (fax) /or e-mail at mark.arnott@nrc.ca

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This paper is a contribution from the National Research Council of Canada, Institute for Research in Construction.
Cet article a été fourni par l’Institut de recherche en construction du Conseil national de recherches Canada