Mobile workforce app saves businesses almost £4m

An award-winning mobile workforce management app aimed at engineers and builders out on the road has saved its customers almost £4m since it was launched in November 2011.

MyMobileWorkers, developed by Momote is the UK’s first pay as you go workforce management app which allows a workforce to accurately log any kind of job information on a mobile phone device which is then fed into a back office system

The app eliminates the need for paper job sheets, saving time for both engineers out on the road as well as the administration time taken to process them.

Altogether the app has saved more than 280,000 hours for its customers, breaking down to £3,455,611 in field service hours and £292,782 in administration time. It has also saved customers £8,393 on the 1,721,900 sheets of paper they didn’t need to use, equating to nearly a tonne. Every tonne of recycled paper saves around 17 trees.

The app is used by companies across a variety of sectors including building maintenance, waste recycling and engineering across the North West and UK.

Suffolk based building maintenance company MC Contracts uses the pay-as-you-go mobile workforce management app to assign, track and record job details for its engineers.

The app has already saved the company 45 man-hours a week as engineers no longer have to travel to and from the head office to drop off paper job sheets. Jobs are assigned in the morning via the mobile device and engineers can get straight out on the road.

Mark Calver, managing director of MC Contracts, whose key contract is with a major housing association, said: “Investing in this new technology has been a huge boost to our company, the unique model of paying per job has meant this is affordable.

“Historically we’ve looked at similar systems and they have been cost prohibitive.

“This model of paying per maintenance visit has allowed us to improve the speed with which we can attend maintenance call-outs which benefits us as a business and also benefits the customer.

"The app means the engineer can access all the correct job information instantly at the touch of a button which saves them having to contact the office repeatedly for job details.”

Graham Whistance, founder of MyMobileWorkers, said: “Saving businesses money and increasing efficiency is one of the main reasons we launched MyMobileWorkers in the first place and the results speak for themselves.

“Mobile apps such as ours allow small businesses to get more time out of their day and spend it on higher value work.

“Tough economic conditions have highlighted the need for companies to pay close attention to the way in which their mobile workforce is managed and the pay as you go aspect of MyMobileWorkers makes it inclusive for businesses of all sizes.”

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New BM TRADA Q-Mark Fire Door Maintenance Scheme provides specifiers with complete peace of mind

BM TRADA Certification has launched a new Q-Mark scheme for Fire Door Maintenance to complement its Fire Door Manufacturer and Fire Door Registered Installer Schemes.

Working closely with sister company Chiltern International Fire (CIF), BM TRADA has responded to considerable demand from both specifiers and installers to introduce this new scheme, which meets all the complex demands of on-site maintenance required under the Regulatory Reform (Fire Safety) Order.

The Q-Mark Fire Door Maintenance scheme has been developed as a result of extensive consultation and a three-month pilot programme.

Commenting on the new scheme, Simon Beer, Product Certification Manager - Doors and Windows, BM TRADA Certification, said: “Previously we have operated an installation scheme that demonstrates competence to install. This new scheme now helps to ensure that the ongoing performance of a doorset is maintained after the initial installation.”

The specific requirements of the scheme include initial training, delivered through CIF’s ‘Fire Doors Explained’ - incorporating additional installation and maintenance modules, followed by a written exam; initial audit; and ongoing surveillance audits. Accepted Repair Techniques are a key part of the scheme, allowing maintainers to repair moderate damage, with traceability back to supporting evidence.

Simon adds: “Together with the Fire Door Manufacturer scheme and Fire Door Registered Installer scheme, the specifier can now be confident that the product, its installation and on-going maintenance are all covered by Q-Mark third party certification.”

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Nanolia's nano coating enables any machine to operate more efficiently, while reducing fuel costs and emissions

Nanolia has introduced a product that enables virtually any machine to operate more efficiently, while reducing fuel costs by around 11% and emissions by around 60%. Based on the latest German nanotechnology the product which is simply added to engine or gearbox oil is a low cost way to reduce the cost of operating machinery – from the smallest motors and generators to the largest marine diesel engines and including pumps, gearboxes and winches.

It can even be used to good advantage to save the cost and extend the life of company vehicle fleets. One application, the company says, is good for 100,000 Kms - even if the oil is changed many times in that period. And after 100,000 Kms, it can be simply reapplied to further the vehicle's life.

The product - which is not classed as a fuel or oil additive - is a nano coating that actually prevents engine metal wear so that gears, pistons and bearings became almost maintenance free with extended service life.

Environmentally Positive

These “smart coatings” are easy to apply and have a major positive impact for factory and plant owners, logistic and fleet operators, helping drive sustainability, efficiency and cleaner air.
* Longer lasting engines / vehicle gears, pistons and bearings
* Fuel Efficiency: around 11% savings on fuel
* Cleaner air / emissions reductions (on average 50-60%)

How does it work?

Theoretically, lubricants work by creating a protective film that avoids direct contact of the metallic surfaces. However, lubricants are not able to protect the metal surfaces under all conditions and permanently. This new nano coating technology works rather differently. It actually modifies the surface texture of frictional metal parts and creates a new, very smooth metal silicate coating. This metal silicate coating reduces friction and increases efficiency, especially in older engines and gearboxes. Due to optimisation of compression pressure in engines, oil- and fuel consumption, emissions and CO2 exhaust gases are reduced.

The synthesized metal silicate compound only has to be added to the original lubricant and is carried to the affected areas of the engine or gear box. In the abrasion area, the metal silicates react due to high temperature and/or high partial pressure and conjoin with the metal surfaces, filling the smallest corrugations, pores or micro cracks in the metal surface, forming an extremely smooth and solid metal silicate layer.

The treated metal silicate surfaces have a much lower friction coefficient and allow for a better and faster build-up of a lubricating film. The effect on wind turbines, for example, is well documented and significant in terms not only of extended gearbox life but also increased power generation.

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H+H aircrete used to build Hospital

H+H’s Celcon Plus Blocks using Thin Joint Celfix Mortar were specified for their impressive thermal properties on both the separating and internal walls for Tŷ Llidiard - Litchard House, the new Child & Adolescent mental health unit at the Princess of Wales Hospital in Brigend, Wales, built by BAM Construction for Abertawe Bro Morgannwg University Health Board.

The exact specification of the blocks used was Celcon Standard and High Strength Plus Blocks in 100, 140 and 215mm thicknesses.

Tŷ Llidiard has been designed to improve the provision of Child Adolescent Mental Health Services in South Wales. The new 3400m² facility provides 19 attractive single-patient rooms with ensuite bathrooms to provide a safe and welcoming environment for patients.

The modern masonry method of Thin Joint construction meant that a frame wasn’t required for this project apart from sections that had large spans, making an overall saving of around £350,000.

BAM Construction began the work in January 2010, Mike Sealey, Design Manager explains, ‘ We needed to build to low U-values for walls and H+H aircrete blocks helped us to achieve this. The dimensional accuracy of the Thin Joint system increased the speed of the entire process. Celcon Plus Blocks are also particularly robust, which is essential for a project like this as the facility will experience wear and tear and is designed to last for a long period of time.’

Mike continues, ‘During my 26 years in the industry I have used H+H blocks on many occasions. My previous experiences with H+H are from within the housing sector, however the blocks fitted the specification perfectly for this hospital. During the course of the build the team received fantastic technical support, particularly from H+H’s Ian Lathbury.’

The £12.325 million Child and Adolescent Mental Health Unit consists of single storey wards surrounding two courtyards with access to the outdoors for emotional wellbeing. The facility also includes music and art therapy, family therapy, occupational therapy, sports hall and pitch, classrooms and an overnight stay area for parents. Mike and the team at BAM Construction completed their phase of the build at the end of May 2012 with patients moving in by the middle of June 2012.

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7 bidder evaluation criteria

Because the construction bid evaluation is limited to price and other price-related factors only, the decision procedure of bidder evaluation criteria is much more simpler than other competitive procurement measures relating  more complicated evaluating factors.

Bid Evaluation Procedure  is carried out in 2 steps. After the bid has been determined responsive, the bidder must be determined responsible as follows.

7 bidder evaluation criteria

In order to be determined responsible, a bidder must be successfully evaluated against the 7 following criteria:

1. Performance Schedule.

The bidder must be able to comply with the performance schedule, required or proposed delivery, taking into consideration all existing commercial and governmental business commitments.

2. Financial Resources.

The bidder must have adequate financial resources to perform the contract, or the ability to obtain them.

3. Performance Record.

The bidder must have have a satisfactory performance history, if any. Nevertheless, a prospective contractor shall not be determined responsible or non-responsible solely because of a lack of relevant performance history, except when specified in a standard for special acquisitions.

4. Integrity and Ethics.

The bidder must have a satisfactory record of integrity and business ethics including satisfactory compliance with laws related to taxes, labor and employment, environment, antitrust, and consumer protection.

5. Construction Machinery .

The bidder must have the necessary technical equipment and facilities for production or construction, or ability to obtain them.

6. Organization and Skills.

The bidder must have the necessary organization and skills, experience, accounting and operational controls, and technical skills, or the ability to obtain them.

7. Other Qualification.

The bidder must be otherwise qualified and eligible to receive an award under applicable laws and regulations.

Bidder evaluation criteria is also known as: bidder Responsibility Determination, contractor responsibility determination, vendor responsibility determination, bidder evaluation worksheet.

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New Worldwatch Institute report discusses worldwide developments in oil production and consumption

Global oil consumption increased by 0.7 percent in 2011 to reach an all-time high of 88.03 million barrels per day, according to new research conducted by the Worldwatch Institute for its Vital Signs Online service. This rate of increase was considerably slower than in 2010, when oil consumption rose by 3.3 percent following a decline of 1.3 percent in 2009 due to the global financial crisis.

China's oil consumption increased by 5.5 percent in 2011, and China accounted for about 85 percent of global net growth in oil use. An increase in oil consumption of 5.7 percent in the former Soviet Union contributed another 37 percent of net growth. But these increases were offset by declines in the United States and European Union, where oil consumption fell by 1.8 and 2.8 percent respectively, writes Worldwatch Climate and Energy Research Associate Shakuntala Makhijani.

The gap in oil consumption between countries in the Organisation for Economic Co-operation and Development and all other countries narrowed further in 2011, with the two groups respectively accounting for 51.5 and 48.5 percent of total oil consumption. Oil remained the largest source of primary energy worldwide in 2011, but its share fell for the twelfth consecutive year to 33 percent.

To meet continued growth in demand, global oil production rose for the second year in a row, by 1.3 percent in 2011, to reach 83.58 million barrels per day. Most of this increase was driven by higher production in countries that belong to the Organization of Petroleum Exporting Countries (OPEC), which overall grew by 3 percent in 2011. Meanwhile oil production in non-OPEC countries fell slightly by 0.1 percent. Oil production growth was slow compared with natural gas and coal production, which grew by 3.1 and 6.1 percent, respectively, in 2011.

Political unrest in the Middle East and North Africa had a significant effect on oil production in certain countries in the region. Output in Libya fell by 71 percent in 2011 from 1.7 million barrels per day (2 percent of global production in 2010) to just 479,000 barrels (0.6 percent of global output) due to the disruptions related to the civil war. At the same time, tense political situations and violence in Iran, Syria, and Yemen resulted in production declines of 0.6, 13.7, and 24 percent, respectively, in 2011.

The global impacts of the April 2010 Deepwater Horizon offshore drilling rig blowout and oil spill have been limited thus far, with reviews in most countries finding that existing safety requirements suffice to prevent similar accidents. Despite expanding offshore drilling efforts, the share of offshore oil is expected to remain steady at 30 percent of global oil production due to declining output from North Sea and Mexican offshore oil wells. Deepwater oil production is expected to constitute a growing portion of this production and is projected to go from 6 percent of total global oil supply today to 9 percent by 2016.

"Against the backdrop of fluctuating oil prices and concerns about supply risk, many countries are paying more attention to their dependence on imports and the stability of the countries they purchase oil from," said Makhijani. "In 2011, the United States imported 60 percent of the oil it needed, Europe imported 90 percent, and imports accounted for 68 percent of China's oil consumption."

The Middle East remains the world's largest oil exporter, accounting for 36.2 percent of exports in 2011 and a growing share of the global market. The Soviet Union and the Asia Pacific region were the second and third largest exporters, with shares of 15.9 and 11.4 percent, respectively. Oil exports from North Africa fell by 32.8 percent in 2011 due largely to the disruptions in oil production caused by political instability in the region. Exports from the United States grew by 19.4 percent in 2011, faster than in any other region, but they accounted for only 4.7 percent of the global market.

Further highlights from the report:

-Oil remained the largest source of primary energy worldwide in 2011, but its share fell for the twelfth consecutive year to 33 percent.

-Average annual prices for West Texas Intermediate crude reached $94.83 per barrel in 2011, close to the average 2008 price of $99.67 per barrel.

-OPEC countries control 72.4 percent of global oil reserves, and the Middle East has the largest share of reserves of any region, at 48.1 percent of the total.

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Personnel from the Corps of Royal Engineers benefit from paver course by Eurovia Surfacing

Recently, personnel from the Corps of Royal Engineers completed a paver course attachment with road and pavement surfacing specialist, Eurovia Surfacing, allowing the corps to design, build and maintain a military road network or airfield when deployed abroad. The students were given a full site safety induction on arrival and spent three days with the Eurovia Surfacing team, benefiting from its expertise and facilities. During this time, Eurovia Surfacing offered its knowledge and experience to fulfil criteria towards the Military Plant Foreman title for which the attendees are training.

“We are extremely grateful to the Eurovia Surfacing team for offering its facilities and resources to train us,” says Sergeant James Collins. “It has been extremely beneficial to learn from experienced pavers how to use equipment and machinery safely and efficiently, whilst applying it all to a real life situation. We will be able to use this knowledge when working on military road and airfield networks whilst deployed, ensuring safer travel routes for the armed forces.”

The students benefited from Eurovia Surfacing’s knowledge of paving and surfacing issues including road construction and paver operations, incorporated with hands on experience working with the Eurovia Surfacing team on a live surfacing project on the A416 near Chesham.

“We were able to help the engineer’s complete hands on activities such as bond coating, rolling patterns, site mobilization and traffic management in order for the corps to apply these skills on military bases elsewhere,” says Peter Oakes, Contracts Manager at Eurovia Surfacing. “Our teams also offered their guidance and know-how in the operation of tandem rollers, paver and chipper machines.” The students learnt first-hand how to install, manage and improve a road network. Students will have completed key criteria to gain their MPF title, ensuring they are of maximum use to the army in the field.

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Six Sigma Project Management

Employing Six Sigma for the business environment is for achieving well-defined goals. The project selected for deploying Six Sigma is not self-sustaining and can develop tendencies to get off target following even the slightest let up in its management. The focus of the Six Sigma management committee is to steer the project implementation to meet those stated goals within budget and time constraints.

Six Sigma Project Management Stages

Project management in Six Sigma begins even before selecting a project. In the run up to the implementation, the right kinds of people, who have proven track records, are selected for Black Belt positions. Since Black Belts are the pillars of managing six sigma, it essential that candidates have proven qualities such as attention to detail, tendency toward problem solving and a proclivity for dedicated work.

Organizational clearances, essential for project implementation, have to be sorted out at this stage. Project selection that has a potential for a high payoff cannot be missed out on any account. For example, because of lack of funds or because of organizational stumbling blocks.

Defining Project Goals And ROI

Defining project goals and estimating pragmatic ROI is essential at this stage to set the course for project implementation and for bringing it back to course if an audit shows that deviations occurred during the implementation. This is really important – if deviations are missed it will produce endless financial and customer base losses to the company. Another key aspect is setting practical ROI targets without getting carried away. The bar shouldn’t be set too high and certainly what has not evolved from the “Voice of the Customer”.

Getting Down To Measurements

Measurements are the watchdogs of a project and demand total integrity. This is the area where Master Black Belts and Champions need to concentrate completely. Black Belts can encounter undesirable pressures for misrepresenting facts, which would otherwise expose a few poor performances.

Another issue that needs to be tackled is of a more serious nature. The consultant teams have their interests in keeping the project going on for as long as possible. This fact may be seen in the fact that Black Belts employed at the company do not measure up to the reputation of the consulting firm. From this point of view, it becomes important to double check and get back to the basics to negotiate the names of professionals who are going to be deployed.

Six Sigma Audit By Internal Committee

The internal audit committee must not the audit exercise lightly, as there is much at stake. The audit committee, besides inspecting process records and documented measurements, must place a lot of emphasis on interviewing the internal customers. The interviews should focus on finding the status of efforts at minimizing customer complaints. This is clearly an exercise of contrasting the condition ‘as is’ against ‘should be’, which is the goal. The Champion will then take over the matter for brainstorming with the Master Black Belts and Black Belts. The agenda of the brainstorming session should not deviate from discussing the findings of the audit committee.

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What are the IS codes used for Clay and Stabilized Soil products for Construction?

Following are the IS codes which are used for Clay and Stabilized Soil products for Construction. It includes standardization in the field of burnt, unburnt clay and stabilized soil products for construction.

IS 654:1992 Clay roofing tiles, mangalore pattern – Specification.

IS 1077:1992 Common burnt clay building bricks – Specification

IS 1464:1992 Clay ridge and ceiling tiles – Specification

IS 1478:1992 Clay flooring tile – Specification

IS 1725:1982 Specification for soil based blocks used in general building construction

IS 2117:1991 Guide for manufacture of hand-made common burnt clay building bricks

IS 2180:1988 Specification for heavy duty burnt clay building bricks

IS 2222:1991 Specification for burnt clay perforated building bricks

IS 2248:1992 Glossary of terms relating to clay products for buildings

IS 2690(Part 1):1993 Burnt clay flat terracing tiles- Specification : Part 1 Machine made

IS 2690(Part 2):1992 Burnt clay flat terracing tiles – Specification : Part 2 Hand made

IS 2691:1988 Specification for burnt clay facing bricks

IS 3367:1993 Burnt clay tiles for use in lining irrigation and drainage works – Specification

IS 3495(Part 1-4):1992 Methods of tests of burnt clay building bricks:
Part 1 Determination of compressive strength
Part 2 Determination of water absorption
Part 3 Determination of efflorescence
Part 4 Determination of warpage

IS 3583:1988 Specification for burnt clay paving bricks

IS 3951(Part 1):2009 Specification for hollow clay tiles for floors and roofs Part 1 Filler type

IS 3951(Part 2):2009 Hollow clay tiles for floors and roofs-Specification: Part 2 Structural type

IS 3952:1988 Specification for burnt clay hollow bricks for walls and partitions

IS 3978:1993 Manufacture of burnt clay Mangalore pattern roofing tiles – Code of practice

IS 4885:1988 Specification for sewer bricks

IS 5454:1978 Methods of sampling of clay building bricks

IS 5779:1986 Specification for burnt clay soling bricks

IS 6165:1992 Dimensions for special shapes of clay bricks

IS 7556:1988 Specification for burnt clay jallies

IS 8920:1978 Methods for sampling of burnt clay tiles

IS 11650:1991 Guide for manufacture of common burnt clay building bricks by semi-mechanized process

IS 13317:1992 Clay roofing country tiles, half round and flat tiles – Specification

IS 13757:1993 Burnt clay fly ash building bricks – Specification

This Indian Standard Code list for Clay and Stabilized Soil products for Construction is updated as on January 31, 2012 on engineeringcivil.com. We have tried to list all Indian Standard Codes for Clay and Stabilized Soil products for Construction, but might have missed a few. If you know any code which we have missed, just comment below and help us add it in this list.

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ISG Knightsbridge Double Awarded by Cadogan

The latest schemes, at 123 Sloane Street and 12 Herbert Crescent by prestigious Chelsea-based property investment company is chaired by Viscount Chelsea, who has taken over recently from his father the Earl of Cadogan, whose family assets make up its portfolio, added to the live projects ISG is currently carrying out for Cadogan at 107-109 Cadogan Gardens and 18 Cadogan Garden.

The fit out of 123 Sloane Street will see ISG carry out a complete refurbishment of the Grade II listed terraced building, which is an 18th century town house retaining many of its original heritage features. The challenging 22-week scheme involves reconfiguration of the internal layout within strict English Heritage guidelines and includes lowering the floor level in the basement to increase headroom.

Structural alterations to the basement and ground floor levels will require ISG to underpin the front retaining wall and a bespoke kitchen and dining area will be created in the newly enhanced basement. ISG will also install highly efficient mechanical and electrical services within the luxury accommodation, delivering advanced A/V, lighting and security systems, as well as an energy efficient climate control installation.

The high specification fit out of the property includes conservation of original features and the installation of reclaimed parquet flooring throughout the common areas. Externally, ISG will construct a link between the building and the client’s neighbouring property and the contractor will also landscape the garden to a new design.

At 12 Herbert Crescent, ISG will carry out a 44-week refurbishment programme that will create a luxury, contemporary town house residence, setting a new benchmark for Cadogan’s rental portfolio. Located close to the world famous Harrods store in the heart of Knightsbridge, the property will retain its external façade but ISG will comprehensively strip back the interior to create a high quality, contemporary residence. The internal fit out will include a fitted wine cellar in the basement, a bespoke kitchen and high specification A/V equipment throughout, including a home cinema.

Externally, ISG will demolish an existing extension to the rear of the property and replace this with a new two-storey structure, which incorporates a roof terrace.

Grahame Roberts, divisional managing director of ISG Fit Out, commented: “These latest projects are part of a continuing programme of estate improvement by Cadogan and the quality of the completed refurbishments combined with their stunning locations will place these properties amongst the most prestigious rental accommodation in the world.

“Delivering the quality of finish required to create such aspirational homes demands a contractor that has vast experience of meeting exacting standards. ISG has the proven expertise to address the challenges of listed building restrictions, enclosed city sites and fast-track programmes, and we are delighted to be building upon our relationship with Cadogan.”

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RCC Mix Design

Mix design proportioning methods for Roller Compacted Concrete RCC:

ACI 207.5R (chapter 2.4) and ACI 211.3R extensively described the mix design proportioning methods for no slump concrete applicable for Roller Compacted Concrete RCC

Materials Used in RCC mix design
a) Cementitious materials:
Cement content is generally low (typically 70 to 130 kg/m3). Any kind of Portland Cement (but low heat cement is a preferred type when its is available)

Fly Ash: Class F pozzolans are preferred. When used pozzolans, may replace up to 80 % of cement content.

b) Aggregates:
Selection of aggregates and control of aggregates quality is essential. Aggregates shall meet ASTM C33 standard.

Coarse aggregates:
Most of project use a coarse aggregates with a Nominal Maximal Size Aggregate (NMSA) between 37.5 and 75mm. The thickness of placement layer shall be more than 3 times the NMSA.

Fine aggregates:
The grading of fine aggregates strongly influence paste requirements and compactibility of RCC. It also affects water and cementitious material requirements needed to fill the aggregates voids and coat aggregate particles.

Other aggregates: Fines (crusher fines…):
In low cement content mixtures, supplements fines (material passing 0.075 mm sieve) are usually required. Fines quantities is generally 5% of total aggregates

c) Admixtures:
Admixtures for RCC needed mostly for set retardation (and plasticizing) effect. Water Reducer Type D (WR + retarder)
WR use is beneficial for strength gain, and retardation which can be required very extended. Main Sika Product for RCC: Plastiment TM 25 specifically designed for RCC.

Mix design considerations:
a) Workability / Consistency:
Measured with a Vebe vibrating table (ASTM C 1170).
The test principle is to measure the time for the concrete to be consolidated by vibrating in a cylindrically shaped mold. The longer the time, the drier/lesser workable is the concrete. Vebe times of RCC mixtures is generally from 10 to 40 seconds. Comparison of concrete consistency measured by slump and Vebe apparatus. ACI 211.3R

Consistency Slump (mm) Vebe (s)
Extremely dry - 32 to 18
Very Stiff - 18 to 10
Stiff 0 to 25 10 to 5
Stiff Plastic 25 to 75 5 to 3
Plastic 75 to 125 3 to 0
Very plastic 125 to 190 -

b) Strength:
Design strength of RCC dam is often based on long term strength (90 days, 120 days or even 1 year!). The strength of RCC is a function of w/c ratio only for mixture with Vebe time of ~ 15 to 20 sec. range. For drier mix, the strength is more controlled by the moisture-density relationship.

If water content is less than optimum => voids in structure, poorly compacted concrete with loss in density and strengths.

Compressive strength of RCC is usually measured by testing cylinder (15cm diameter, 30cm long).

Strength measured on cores is also possible.

d) Segregation:
It is necessary to produce mixture with minimum tendency to segregate => Aggregates (especially with NSMA > 37.5mm) shall be well graded.

Higher cement content mixture are generally more cohesive => less tendency to segregate.

e) Permeability
Mixture with paste volume of 18 to 22% by mass shall provide suitable level of impermeability. Higher cementitious content or high workability mixes that bond well to fresh lift joints will produce watertightness.

For lower cementitious content mix, and/or low workability mix, a bedding mortar between lifts may be needed.

f) Heat Generation:
It is an important factor considering the massive structures. Limitation of cement content, and/or use of fly ash is helping reduce heat generation.

g) Durability:
RCC should be free of damaging effects of alkali-aggregate reactivity

Quality control of RCC concrete:
Vebe Consistency Test
Density and air voids tests.
Moisture/water content tests.
Cement content evaluation
Temperature monitoring
Test (cylinders) specimens:
- Using modified Vebe apparatus (generally for mix with Vebe up to 20 seconds),

- Using of special vibrating hammers

Beware, because of low early strength of concrete specimens are “fragile”.

Lift-Joint sealing systems:
Lift joints shall be kept moist before placing next lift and normally do not require special treatment. In some cases, it is required to apply a “flowable” bedding mortar which need to be retarded with admixtures.

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Concrete Mix Design Secrets

In order to make a concrete mix design that works, you should master all the concrete theories in combination with experiences of concreting at work. Here is some important things you need to know when design concrete mixes.

A. What do you need to know before designing concrete?
1. What are the strength requirements?

- Compressive (on cube or cylinder specimen) strength

- Flexural strength

- Tensile strength

2. What is the placing method? By pump or direct pouring?

3. How far is the job site from the batching plant?

4. What is the structure for casting? Pavement, foundation, elevated slab, etc.

5. What are the projects specification?

- Maximum or minimum cement contents

- Maximum water/cement ratio

- Slump or consistency limit

- Minimum Strength requirement @28 days

- Material specifications (what is the maximum size of aggregate?)

6. Latest testing results of materials is needed in the preliminary selection of materials and design calculation

B. What are Design Precautions and Things to Remember when design concrete mixes?
1. Increasing the sand/total aggregate ratio, increases the water requirement at the same consistency.

2. Increasing the water/cement ratio decreases the strength of concrete at the same cement content.

3. Remember that adding 5 liters of water per cubic meter increases the slump by 2.5cm.

4. Remember that adding 5 liters of water per cubic meter decreases strength by approximately 4%.

5. Always follow recommended admixture dosage.

6. Always have “control” when performing trial mixes, always perform trial mixes with another mix using the same materials. This data can be useful in diagnostics if a problem occurs.

7. Always adjust batching quantities to the actual moisture condition of the aggregates.

8. Volume tolerance for 1m3 concrete is 1 ± 0.2m3.

9. Range of normal weight concrete is from 2,200 kg/m3 to 2,400 kg/m3

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9 Questions Before Making Shotcrete Mix Design

Before making a mix design for shotcrete or sprayed concrete, it is needed to get sufficient information from the clients. Adequate support information will be resulted in technically and economically effect for the work. A proper mix design assure a successful trial and thus, successful application on site.

Hereafter is a list of 9 questions to the ask the clients prior to making a shocrete mix design:

1. The location of shotcrete to be applied? Slope stabilization, overhead and wall in tunnel
2. Wet or Dry process will be applied? Normally, dry process for slope stabilization, wet process for tunnel lining.
3. The requirement of early strength (8 hours, 72 hours, 7 days, 28 days) and the final strength at each location.
4. Slump requirement (for wet process only)
5. What accelerator admixture to be used? Please note that it would be better to use liquid admixture in rainy season.
6. What is the concrete spraying machine to be used? Rotor Machine (for both wet and dry process) or Pump Machine (wet process only)
7. What kind and type of cement to be used (cement should be super fine. Blain Surface fineness is greater than 4000 square centimeter per gram) PC cement is most suitable for early strength requirement.
8. A dispenser system need to be installed in case wet process is used. Is such liquid dosing unit available?
9. Any other information is helpful in designing shotcrete mix?

Once these question get answered, the mix designing process can be started. For shotcrete or sprayed concrete, trial is a must be prior to the issue of mix design for actual application.

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What is shotcrete?

Shotcrete or gunite was invented by Mr. Carl Ethan Akeley (1864-1926) in 1910. For attractions of a park, this American Architect was mandated to realize in concrete the reproduction of a dinosaur. Considering the sizes of the structure, he had the idea to develop a “cement gun” machine allowing the spraying of a cementitious mortar. Shotcrete was created!

Probably a symbolic coincidence, but the same year, Mr. Kaspar Winkler founded Sika. Since that time Sika has greatly contributed to the development of the shotcrete technology. By shotcrete technology development, we mean the continuous development of chemical additives and admixtures for shotcrete and as well the development of spraying equipments.

Fields of shotcrete application
Shotcrete is mainly used in Underground construction projects as preliminary or permanent structural support. By Underground constructions, we mean the construction of structures like road-rail tunnel, hydropower plant, mines, parking, subway, metro, storage area etc.
However shotcrete is as well as an economical tool to realize stabilization work (slope), swimming pools, waterways, concrete repairs, inner lining and architectural structures. About 90% of the shotcrete applied goes into Underground construction projects. Total volume of shotcrete worldwide applied yearly is more than 12 millions cubic meters

What is shotcrete?
As per the American Concrete Institute (ACI), shotcrete can be defined as a mortar or concrete, pneumatically projected at high velocity through a pressure resistant conveying line onto a surface, where it is compacted on impact.

Cement, sand, aggregate, water, additives and admixtures are the components entering in the production of the shotcrete mix.

Compared to normal concrete, shotcrete differs mainly from three points:

The maximal size of the aggregate used.
The way to place it.
The mixture of shotcrete can be dry or wet.
Regarding terminology we can describe Gunite as sprayed mortar while Shotcrete as a sprayed concrete.
By gunite we means a cementitious mixture of which the particles size is limited to 8 mm.
For shotcrete we consider the use of aggregates of which the maximal size is 16 mm. However, in the last 10 years there is a tendency to limit the maximal aggregate size to 12 mm.

Shotcrete development can be summarized from its start to nowadays as follows:
Dry process –> dry process with powder accelerator –> wet process with Alkali liquid accelerator –> wet process with Alkali free accelerator.

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Shotcrete mix design and proportion

Aggregate

Aggregates for shotcrete my contain river sand, crushed sand and crushed stone with particle sizes up to 16mm, normally up to 9.5mm.

Here after is a typical and recommended gradation of combined aggregates for shotcrete that will resulted in perfect mix design.:

Water Cement Ratio

The water-cement ratio for wet shotcrete normally falls within a range of by weight and 0.40 to 0.55 for wet-mix shotcrete.

Dry mix design shall only include water content enough for the hydration process of cement needed for strength development.

In dry-mix shotcrete, the moisture content of the fine and coarse aggregates should be such that the aggregate-cement mixture will flow at a uniform rate, without slugging or hose plugging. The optimum moisture content is generally within the range of 3 to 6 percent. The sand should be dried or wetted as required to bring the moisture content within that range. Large fluctuations in moisture content should be avoided.

A crude but effective test for determining proper predampening is the “ball-in-hand” test. A small amount of mix is placed in the hand and squeezed tightly. When the hand is opened, the mixture may crumble into discrete particles which indicates too little predampening moisture and is usually light gray. If the material holds together, or cracks but remains essentially whole, there is enough moisture. If moisture comes off on the hand, there is too much moisture in the mix.

Unit Weight of Concrete

The unit weight of good shotcrete is usually between 2230 to 2390 kg/m3, about the same as conventional concrete.

Cement Content

OPC cement with surface Blaine above 4500 cm2/gr is most suitable for shotcrete. Typical and recommended cement contents is:


* It is in the best interest of the end user to perform trial mixes and shotcrete trial to determine the suitable cement content, to meet other parameters, above table is used only as a guide in preliminary design and shall be decided in the results of trial mixes and trial application.

Proportioning

Shotcrete design for wet process can be designed like conventional concrete but these mixes contains higher volume of fine aggregate and cement. Shotcrete process can be designed by absolute volume method or by weight.

Shotcrete design for dry process is designed using the bulk densities of the materials, usually the water content is not included in the calculation.

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Application of sprayed concrete or shotcrete

Uses of sprayed concrete (or shotcrete)
Over the past century, sprayed concrete has replaced the traditional methods of lining tunnel profiles and has become very important in stabilizing the excavated tunnel section. Sprayed concrete is a single term that describes various component of a complete technology:

the material sprayed concrete
the sprayed concreting process
the sprayed concrete system
Sprayed concrete construction is used in many different types of project. The flexibility and economy comes to the fore in above-ground and underground buildings, tunneling and special underground construction, in fact throughout the construction industry. The following uses are widespread:

excavation stabilization in tunnelling and underground construction
tunnel and underground chamber lining
stabilization in mine and gallery construction
concrete repair (concrete replacement and strengthening)
restoration of historic buildings (stone structure)
sealing works
trenching stabilization
slope stabilization
protective lining
wearing courses
special lightweight load-bearing structures
creative applications
In terms of importance, tunnelling, mining and concrete repair head the list. In tunneling and mining, the main uses are for excavation stabilization, temporary and permanent arch lining. Sprayed concrete is also used fir all other appropriate concrete works. Large cavities are often spray filled, for instance. Spray concrete has confirmed and strengthen its position alongside tunnel segment lining (tubbing) and interior ring concrete as the main concreting method. The limits on its use lie in the technical and economic interfaces with the other concreting process and/or construction methods.

Types of construction using sprayed concrete (shotcrete)
Sprayed concrete is used in all areas of tunneling construction – for road or rail tunnels, water drainage and underground military structures, in addition to slope stabilization. Whether tunneling under a building or driving through an obstruction, the construction method is determined by the weight-bearing properties and stability of the substrate tunneled through. The main distinction is between full excavation of the entire section in one operation and partial excavation in many different forms and methods. If full excavation is not possible due to the rock stability, the final profile is often excavated is several phases.

In underground construction, because high stresses would often be exerted on the newly places excavation stabilization and lining. Predetermined deformation of the excavated section is often allowed and only then is the stabilization given a non-positive seal. This causes the stress to be distributed around the excavation section and in the area around the excavation face.

Keep reading next coming post: Sprayed concrete for stabilization and lining.

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Fibre Reinforced Concrete

Conventional concrete containing discontinuous discrete fibres is called fibre-reinforced concrete. Fibers of various shape and size produced from steel, plastic, glass, carbon and natural materials have been used.
However for any reinforcement to be effective, it must be stiffer than the concrete matrix that is reinforcing. Generally the less stiff fibres (made from plastic and natural materials) only offer benefits in improving the tensile strength of plastic and semi-hardened concrete and are therefore mainly used to reduce plastic shrinkage and plastic settlement cracking. The stiffer fibres improve both the tensile strength and the toughness of harden concrete.

The most widely used stiff fibre is steel. Low volume fractions of fibres (less than 1%) are used to reduce shrinkage cracking. Moderate volume fractions (between 1% to 2%) increase flexural strength, fracture toughness and impact resistance. High volume fractions (greater than 2%) lead to strain hardening of the composites. The shape and length of the fibres also play a role in the fibres’ effectiveness in improving the properties of the concrete. The use of fibres in concrete can have a marked effect on the workability of the concrete and this need to be taken into account in the mix proportion of fibre-reinforced concrete.

Currently a great deal of research is being undertaken into the use of ultra-high-performance fibre-reinforced composites. One of the benefits of these materials is extremely high ductility. Fibre-reinforced concrete has been used for precast panels, airfield and highway pavements, industrial floors and in spraying concrete for slope stability and underground mining applications.

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