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    Joints are not the problem; Cracks are!

    June 23rd, 2017 Posted by Blog, Concrete Repair, Concrete Repairs, Joint Sealing, Reinforced Concrete 0 thoughts on “Joints are not the problem; Cracks are!”

    Joints are placed in concrete pavement to accommodate slab movement and to prevent natural cracking. The theory is that cracking will follow along the joints if they are correctly positioned.

    The first concrete pavement slabs had no real design and no crack control joints or dowels and no steel reinforcement.

    In the first part of the 1900s Joint Reinforced Concrete Pavement appeared containing steel reinforcement mesh to hold cracking tightly. Then followed Jointed Plain Concrete Pavement using contraction joints to control cracking with no reinforcement steel and dowel bars were introduced to transverse joints to assist in load transfer in 1917. In 1923 Continuous Reinforced Concrete Pavement was introduced whereby transverse cracks are allowed to form but are held tightly together with continuous reinforcing steel.

    Joint Spacing

    Joint spacing is very important in crack control as cracks can form naturally during the curing process without suitable control joints in place.

    The formula for maximum joint spacing is the relationship between:

    • The radius of relative stiffness (mm),
    • the modulus of elasticity of concrete (Mpa)
    • the slab thickness (mm),
    • the modulus of subgrade reaction (Mpa/m),
    • Poisson’s ratio for concrete, usually 0.15.

    Saw Cutting

    There is a short window of opportunity for saw-cutting joints in slabs. Too early and you get ravelling of the joint and the faces are torn and damaged. Too late and the internal stresses causing cracking have already started randomly in the slab.

    The saw cut depth and timing is critical for joint formation.

    Types of Joints

    There are several types of joints which can be transverse or longitudinal in direction:

    • Contraction Joints
    • Construction Joints
    • Isolation Joints
    • Expansion Joints

    All are designed to induce or control cracking.

    Joint Sealants

    Joint Sealants are used to minimise infiltration of surface water and incompressible material into the joint. Unsealed joints can allow sub-soil washout and voids to form and uneven subsidence of slabs resulting in differing RLs and rough transitions across joints.

    Dowel Bars

    Dowel Bars are used to control the joints and their alignment and spacing is critical. If dowels are misaligned and both ends of the dowels are locked in the slab concrete failure and cracking will result. The absence of dowels may cause the transitions across joints to become uneven when the adjoining slab moves out of level or concrete curling occurs.

    Dowel racks are an excellent innovation as they ensure that the dowels are aligned correctly and held in place during the concrete pour.

    Sub-base

    The sub-base material must be compactible and pumping of water through the sub-base through un-doweled joints needs to be eliminated.

    Curing

    Proper curing practices delay the development of these internal stresses, controls internal temperature, delays moisture evaporation, and fosters the development of increased strength.

    Curing therefore controls the evaporation of moisture during the concrete setting process and helps to prevent premature drying of the surface which can prevent or delay the evaporation of the remaining moisture below resulting in an uneven set and issues with strength and surface dusting.

    Steel Reinforcement

    The correct placement of steel reinforcement bars and mesh is critical to provide strength, reduce width and frequency of cracking and hold slabs together whilst setting and under load.

    Typical Jointing Problems

    • Concrete sawing too early causing ravelling or spalling
    • Concrete sawing too late causing early-age cracking
    • Concrete cracking due to insufficient joint depth
    • Concrete cracking due to excessive joint spacing
    • Concrete cracking due to excessive unrestrained warping
    • Concrete cracking due to too much edge restraint
    • Concrete cracking due to excessive slab to sub-base bonding
    • Concrete cracking due to misalignment of dowel bars
    • Concrete cracking due to lack of consideration of weather conditions
    • Sealant not adhering to joint faces
    • Sealant pulls out during operation
    • Sealant gelling
    • Sealant cracking or debonding
    • Voids of bubbles in sealant
    • Water pumping into sub-base
    • Sub-base washout
    • Concrete slab moving out of level

    The Solution

    FCS Concrete Repairs are fully resourced to Inspect, Test, Diagnose and make informed recommendations on the best permanent and cost effective methods to rectify any concrete cracking and maintenance issues. Joint repair and reinstatement is our forte!

    Ref: All About Concrete Pavement Joint Design & Construction
    September 19, 2013, Eric Ferrebee, EITTechnical Services Engineer, ACPA

    Are Pyramids Made Out of Concrete?

    April 4th, 2017 Posted by Blog 0 thoughts on “Are Pyramids Made Out of Concrete?”

    Are Pyramids Made Out of Concrete?

    The website reveals how Ancient Egyptians built the pyramids using man-made stones, which look exactly like natural rocks. The limestone blocks were cast in situ, employing an advanced technology that was later lost, leaving a puzzle hidden for thousands of years inside the pyramid stones. This theory undoubtedly shed an amazing new light on what really happened in Egypt in that remote era.

    The Pyramids at Giza have more than 5 million blocks of limestone, until now believed to be CARVED stones, new evidences shows they were CAST with agglomerated limestone concrete.

    The scientific background, including analysis, formula, stone making, are disclosed in the recently updated book by Prof. Joseph Davidovits Geopolymer Chemistry & Applications, in several chapters, i.e. Chapters 5, 11, 13, 17 and 20.

    Paleomagnetism study supports Pyramid geopolymer stone

    A recent scientific study published in the renown “Europhysics News“, The Magazine of the European Physical Society, (2012), Vol. 43, number 6, described how paleomagnetism study on several pyramid stones demonstrates the validity of Davidovits’ theory on the artificial nature of Egyptian pyramid stones.
    Two scientists, Dr. Igor Túnyi from Geophysical Institute SAS – Bratislava (Slovak Republic) and Ibrahim A. El-hemaly from National Research Institute of Astronomy and Geophysics – Cairo, Egypt, made the following assumption (quote from their scientific paper):

    Our paleomagnetic investigation of the two great Egyptian pyramids, Kufu and Khafre, is based on the assumption that if the blocks were made in situ by the geopolymer concrete technique described above, then their magnetic moments would all have been parallel, oriented approximately in the north-south direction. However, if the pyramids were constructed from blocks transported from the nearby quarries, having been rotated randomly during transport and construction, then the directions of their magnetic moments would be oriented randomly

    Conclusion:

    The aim of paleomagnetic investigation of the rock material of the great Egyptian pyramids, Khufu and Khafre, was to find out the directions of the magnetic polarization vectors of their building blocks. This is one of the possible ways to verify the hypothesis according to which the blocks were produced in situ by a concrete technique. The analysis of a limited set of paleomagnetic samples provided the following results. The paleodirections of three sampling locations (2 from Khafre and 1 from Khufu pyramid) exhibit the common north-south orientation, suggesting that they may have been produced in situ by a concrete technique. The block from one sampling location of the Khafre pyramid is of natural limestone and evidently comes from the adjacent quarry. It is likely that the block from one sampling position of the Khufu pyramid comes also from the same quarry. Finally, we conclude that even if the geopolymer concrete technique was used, the pyramids were constructed from a mixture of natural and artificial limestone blocks.

    See: Igor Túnyi and Ibrahim A. El-hemaly, (2012), Paleomagnetic investigation of the great egyptian pyramids, Europhysics News43/6, 28-31.

    In his book “Why the Pharaohs built the Pyramids with Fake Stones“, Professor Davidovits has clearly shown the location of the natural limestone blocks and terraces (see essentially the Circuit of the Pyramid Plateau at Giza, Egypt, pages 233-262). For example, we know that in the pyramid of Khafre, more than a quarter of the volume of the pyramid is natural stone, namely the terraces carved in the inclined limestone plateau and which constitute the first 5 layers of the pyramid. The book is available at the Geopolymer SHOP and www.amazon.com

    News

    April 4th, 2017 Posted by Blog 0 thoughts on “News”

    FCS Concrete Repairs Pty Ltd has been accepted for Corporate Membership of the Industry Association, the Australasian Concrete Repair Association Ltd.

    The Australasian Concrete Repair Association (ACRA) was formed in 1991 with the aim of providing a forum to promote discussion and an exchange of views in the concrete repair industry to advance the technology and practice of concrete repair and associated activities.

    The Association’s members are at the forefront of concrete repair technology worldwide and include companies and individuals with an interest in repairing and protecting concrete, including:

    • Specialist consultants and engineers
    • Specialist repair contractors
    • Specialist materials suppliers
    • Asset owners

    FCS Concrete Repairs’ latest Equipment Addition

    April 4th, 2017 Posted by Blog, Main Feature 0 thoughts on “FCS Concrete Repairs’ latest Equipment Addition”

    Bunker S8EVM Grout Screw Pump with Mixer

    for small scale spray-cretingin shotcreting and spray applied concrete repair applications.

    The Bunker Grout Pump will be used to apply such products as

    Fosroc Guncrete E: Spray Applied Repair Mortar

    FCS Concrete Repairsstaff are trained and equippedto carryout small scale concrete repair with spray applied repair mortar using the Gunite type process.

    Fosroc Construction Chemicals use Sprayset Chemical,a chloride free liquid based on a blend of inorganic powders, which is added to a sprayed concrete mix to impart properties of high build and low rebound. Its pH level is neutral.

    Fosroc Guncrete E product is a high strength, low shrinkage, high build cementitious spray applied mortar supplied as a ready to use powder for use with standard dry spray or shotcrete equipment.

    The advantages of using the Gunite system with Guncrete E are:

    • High build material
    • High early strength
    • Low drying shrinkage
    • Low rebound
    • Chloride free

    Guncrete E has many applications in the concrete repair industry. Examples where Guncrete E can be spray applied for concrete repair:

    • Bridge Repairs: Concrete cancer type repairs to bridge support columns. Concrete can be reinstated using sprayed mortar such as Guncrete E.
    • Concrete ceilings/soffits. Quality repairs can be achieved using sprayed mortar in small patched areas using the Gunite process.
    • Large area concrete repairs. Concrete repair can be carried out cost effectively on a large scale using spray applied repair mortar.
    • Sea Wall Repair. High build spray applied mortar can be applied to repair deteriorated sea walls because of its quick setting characteristics.
    • Pool Repairs. Ageing concrete pools can be effectively repaired by recoating using the Gunite technology.
    • Concrete Walls. Repair spalling concrete caused by the penetration of water into the concrete can be repaired using the spray applied mortar after removing concrete using torbo-blasting methods.
    • “Drummy” Concrete. Where concrete render has delaminated large areas can be repaired using spray applied mortar.
    • Deteriorating foundations can be repaired effectively using spray applied mortar.
    • Expansion Joint. Overhead repair of spalled expansion joint in a carpark can be repaired effectively using Guncrete.
    • Concrete Beams. Structural concrete beams in suspended decks can be repaired effectively using small scale spray applied mortar methods.

    Before dry-spraying the repair mortar it is necessary prepare the areas before the application of the mortar. This may be achieved by the various preparation methods such as wet grit blasting, torbo-blasting,cleaning and corrosion treatment or replacement of steel reinforcement.

    Steel reinforcement primer may be used with NitoprimeZincrich, a single component zinc-rich epoxy resin specified by Fosroc.

    Guncrete E spray mortar may be used for decks, slabs, horizontal and vertical concrete surfaces to be repaired in one or more layers, each layer 10-150 mm thick where compressive strength >45 MPa compressive strength in 28 days and a low level of drying shrinkage measured to ASTM modified 23°C/50%RH shall not be greater than 500 microstrains at 7 days and 700 microstrains at 28 days is required. The minimum depth for repair shall be 10 mm.

    After applying the sprayed repair mortar the area is finished by striking off with a straight edge and trowelled or floated to achieve a level flush with or slightly proud of the surrounding surface.

    Spray applied repair mortar is cost effective in repairing small scale areas of concrete where hand repairs may be more labour intensive and costly.

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