CEE Oct-Dec 2012

Department. "Planning and preparation of estimates for construction of these roads are on," Borah said, adding, "Reconstruction of the roads with new construction methods will begin between November and December. Our plan is to complete 50 per cent of the 202 shortlisted roads by March, next year." GMC has received Rs. 427 crore from the Kamrup (Metropolitan) Zila Parishad for road construction in the wards under GMC's jurisdiction. While interlocking concrete block pavements will replace small bitumen roads, concrete pavements will be constructed for broad road in the city, Borah said. Courtesy: The Times of India Guwahati, 15.09.2012. Durable concrete is required for long lasting tunnels CHANGING NORMAL CONCRETE INTO DURABLE CONCRETE FOR TUNNELLING I I The author EugenKieen of Mc-Bauchemie Mueller GmbH and Co. KG looks at the materials required to change normal concrete to durable media resistant concrete for use in tunnelling application. The main materials, which can help change normal concrete to durable aggressive media resistant concrete, are: New generation PCE based admixtures Condensed silica fume or microsilica slurry or Latest generation aluminosilicate. PCE based admixtures Most of the new generation superplasticizers are from the Acrylic Polymer (AP) family. Polycarboxylate is a common term for the substances that are specifically used as Polyacrylate or Polycarboxylate ether (PCE). The PCE based Super Plasticizers are by far superior to the conventional once with respect to initial slumping as well as slump retention with time. The efficient working of these plasticizers is due to the new type of molecule designs. PCE based superplasticizers produce excellent properties when used with cementitious materi als. The disadvantages associated with longer setting times of conventional superplasticizers is offset by PCE based super plasticizer and therefore its use in concrete can also attain high early strengths. The development of highly effective superplasticizers with long and consistent duration of action is therefore an important precondition for the production durable concrete, due to low water contents and high early strength requirements. Concrete additives based on PCE offer advantages like: Significant reduction of the water demand of the mix Little loss of consistency Short setting times • High early strengths Low tendency to segregation The advantages of these new generation polymers are very clear, not only in terms of performance but also in terms of the dosages used for similar conditions and this factor balances the disadvantages in economy, as new generation superplasticizers are relatively expensive per unit price. Condensed silica fume/microsilica: The term 'microsilica' is adopted to characterize the silica fume, which is used for the production of concrete. Microsilica or Condensed Silica Fume (CSF) is a by-product resulting from reduction of high purity quartz with coal in the electric arc furnaces used in manufacture of sil icon, ferrosilicon and other alloys of silicon. There are three main reasons for the incorporation of silica fume as an additive for HPC. Microsilica has a filter effect i.e. very fine particle distributed itself in the space between the materials in the concrete in a homogenous way to give rise to more dense concrete. Silica fume imporves the strength of the transition zone between cement paste and aggregates. CSF is highly pozzolanic in combination with Portland cement. 56