The common distress in dams is excessive seepage through body of the dam. The reasons for such distresses are use of poor-quality construction material, environmental problems, constructional deficiency, poor quality control, etc. The repairs to these dams for effective seepage control should be taken after proper diagnosis and investigations. Apart from this repair materials and appropriate repair methodology play a vital role in effectual rehabilitation of distressed dams.
Poly Ironite Ceramic Cementitious (PICC) Mortar for Repairs to Dams :
PICC mortar manufactured by Dimple Chemicals & Services Pvt Ltd, Pune is a mixture of NICOMIX 100 and ordinary Portland cement preferably 53 grade in the ratio 65:35 with water maximum 10 parts. The product is dissimilar from polymer impregnated or polymer modified ones. The polymer used here is to improves bridging capacity of ingredients and to improve porosity. The properties of PICC are evaluated at Governmental Research Stations and Institutes for assessing the suitability of product for its use for rehabilitation of hydraulic structures. The properties are determined as per relevant ASTM, European standards and the Indian Standards and are found well fitted for the requirements of repairs to hydraulic structures as per norms in these standards. The test values obtained as per each of these standards are consistent.
Apart from the good strength properties like, compressive strength, tensile strength, shear strength etc. PICC exhibits permeability of the order of K<10-12 and porosity 1% which is much lower than even high-performance concretes. The mortar is non-shrink, UV resistant, non-toxic and has good resistance to chemical and marine attack. PICC is an inorganic compound highly resistive to chemicals- acids and alkalis. The mortar is easily workable on any type of repair surface i.e. vertical, horizontal or inclined surface. It has good resistance to abrasion as compared with concrete. It adheres very well to rock, concrete, steel and even plastics. The application is monolithic needing no expansion or contraction joints. The important factor to note about the PICC is produced using major ingredients that are found in its final form on the earth and hence the repairs using PICC are certainly durable which is vitally needed in repairs of dams and major hydraulic structures.
Applications of PICC Mortar:
On the basis of the properties, workability and durability and its resistance to Ultra Violet rays. PICC is widely used for repairs of hydraulic structures, like dams, aqueducts, etc. The successful use of PICC since 2009 for “T” pointing of joints in masonry dams, coating of damaged concrete surfaces etc. has proved its effectiveness and durability in strengthening of dams and structures
More than 20 dams covering an area of 1,00,000 m2 has been repaired across many states in the country during last 3 years. The main dams and other hydraulic structures rehabilitated are Salauli dam, Anjunem dam, Almatti dam, Krishnarajasagar dam, Harangi dam, Kabini dam, Hemavaty dam, Kutuhole Barrage, Shorayar dam, Emerald dam, Hirenholi dam, Chandpata dam, Kundah Dam, Eravangalar Dam, Highways Dam Perriyar Forebay, Upper Aliyar, Upper Kothalyar, Hattikuni dam, Markendeya. These repair include pointing of masonry joints, resurfacing concrete surface, resurfacing piers etc. The major and critical repairs are for Krishanrajasagar dam, Mysore and the Markendeya dam. Typical case studies highlighting use of PICC are enumerated below.
Salauli Dam, Goa, India – Repairs to Baffle Blocks:
Salauli Dam is located at village Salauli in Sanguem Taluka of South Goa District. The dam is constructed across river Salauli, a tributary of river Zuari. It is a composite dam consisting of earthen portion of 959 m in length and 42 m in height having a central masonry spillway in river gorge portion which consist of upstream duck bill spillway wall & trough for energy dissipation, hump weir with spillway glacis connected to the downstream stilling basin arrangements. The duck bill spillway is first of its kind in India. Because of peculiar shape of spillway allowing high flow within a narrow width, two baffle blocks each of size 5 m x 5 m x 2.4 m (approx.) are provided en route of water to stilling basin for dissipation of energy. The baffle blocks, the stilling basin and the wave blocks showed signs of distress in the form of cavities in concrete, exposing reinforcement bars, pitting of surfaces and pot holes (Photo 6 & 7). The cause of damages was reported to be due to passing over of high flood of magnitude 510 cusecs.
The PICC was tested by CWPRS and repairs of the two baffle blocks using PICC were done in the year 2008. The damaged blocks before and after their repairs are shown in photo 8. The underwater photography of these block after three years of repairs indicated repaired portions undamaged and hence repairs using PICC proved to be effective.
Gtidc Aqueducts, Goa, India-Resurfacing and Treatment to Joints:
A number of aqueducts under Goa Tillari Irrigation Development Corporation, Goa were reported to be in damaged condition. Photos below show the damages resulting in excessive leakages in one of the aqueduct namely Nanoda aqueduct.
On the basis of tests by CWPRS, the aqueduct was rehabilitated using the PICC mortar by resurfacing internal damaged surfaces and sealing construction joints using elastomeric sealants. Repairs were effective in arresting leakages through the aqueduct. The damaged and rehabilitated aqueduct are shown in photos below.
Kutuhole Barrage, Madikere, Karnataka, India-Resurfacing of Concrete Surface:
Kutuhole barrage serves to store water for use in Madikeri city. It is an old barrage constructed in masonry using lime mortar. The length of barrage is 21m and height 5.5m. Though the upstream face was given a coat of cement concrete of grade M 20 to a maximum thickness of 100 mm by providing 12 mm diameter anchor bars, heavy leakages were through the body and concrete septum. It was once decided to abandon the barrage for use as it was not serving for its intended use.
The repairs were carried out by resurfacing the full upstream face and part of downstream surface by PICC coating of 10 to 12 mm thickness and grouting main body using NICGROUT. The barrage after repairs is performing well and is shown in photo above (right).
Krishnarajasagar Dam-Pointing of Masonry:
Krishnarajasagar dam is one of the principal dam in south India. It is multipurpose project formed by the construction of a dam across the Cauvery river. The length of the dam is 2621 m and height 42.67m. The project authorities observed many distresses on the visible areas like peeling of pointing material giving way to water. Due to washing away of pointing material and mortar filling inside, cavities have formed in the body of dam. The openings of masonry joints were found to be wide and deep as shown in photos below.
Central Water & Power Research Station, Pune, India officials had inspected the site in 2012 and had suggested repair methodology using PICC as repair material for pointing of masonry in addition to grouting dam body. Accordingly, the repair works using PICC was taken up. About 45,000 m2 of upstream area has been treated by pointing masonry joints. The application was awarded an excellency award by DRIP authority. The pointing in progress and pointed surface using PICC is shown in photos below:
- The bonding properties of PICC mortar with cement mortar and rock and its easy applicability makes it most ideal material for pointing of masonry joints
- The porosity (<1%) and permeability (K<10-12) of PICC mortar is very low, which indicates it appropriateness for coating of damaged concrete surfaces like upstream surface of gravity dams which are vulnerable to seepage.
- Excellent bonding properties with concrete, high abrasion resistance and easy application in thin layers makes PICC most suitable for lining of aqueducts, canals, siphons and water conducting systems.
- The ingredients of PICC are in their final form constituting 90% of mortar, hence the mortar is not expected to deteriorate with age provided all precautions are being taken while using the mortar.
- The performance of PICC since 2009 at different sites of work clearly indicates PICC a suitable and durable repair mortar for pointing, resurfacing of hydraulic structures.