Indian Concrete Journal

Grouting materials and practices for century-long corrosion protection of post-tensioned concrete bridges Karthikeyan Manickam, Radhakrishna G. Pillai

Typically, the post-tensioned (PTd) concrete bridges have an anticipated design life or corrosion-free service life of 100+ years. This paper highlights some of the concerns associated with the grouts and grouting practices, which have resulted in a large inventory of inadequately grouted PTd systems. Then, the relevant material properties and associated performance tests to qualify post-tensioning (PT) grouts are discussed. An experimental program on the fluidity, bleed resistance, volume change, and compressive strength of three commercially available PT grouts and one in-house developed PT grout is presented. Then, a compilation of existing standard specifications for PT grouts is presented. Following this, a set of comprehensive, and stringent performance specifications for PT grouts–to enable complete filling of PT ducts–was proposed. Finally, good grouting practices to achieve century-long corrosion protection for PT systems are recommended.

Development of sustainable microbial coalesce bio-cement mortar blended with powdered seashells Veena Kumara Adi

The 3 R’s of reduce, reuse and recycle applicable to civil construction works are warranted. Integration of waste management on a microbial platform is an attractive avenue for research. In this study, the applicability of waste seashells and the urease producing microbe, Sporosarcina pasteurii in cement mortar is explored. This designer mortar was prepared by blending seashells (5 % replacement of cement and sand); and integrating with a microbial inoculum. The mechanical properties and microanalysis of this designer mortar were compared with those of a control cement mortar. The microbial blended cement mortars encouraged the performance of concrete. The results supported sustainability, which is the most urgent need. This study serves and promotes an alternative method for disposal of seashell waste through green technology, management and sustainability.

Studies on the effect of a tree pod based natural plasticizer on durability behavior of concrete Amrutha D. Shenoy, Ravindra R.

This paper describes the results of a comparative study between concrete mixes containing natural plasticizer (NP) and chemical plasticizer (CP) as well as the control mix concerning durability performance. NP used in this investigation was prepared from the extract of rain tree pod and used in concrete. Tests on resistance to acid attack, water absorption, chloride ion penetration, water permeability, and sorptivity were carried out as per codal provisions. The chloride permeability of concrete was moderate with the addition of the developed natural plasticizer. The strength decrease of cubes subjected to acid attack with the addition of NP was lesser in comparison to the control mix. The results obtained show that the concrete mix with NP exhibited better performance than the control mix and worked equally efficiently as the mix with CP with respect to durability. Therefore, the NP prepared from the rain tree pod extract has the potential to be used as an alternative to CP for enhancing durability of concrete.

Elastic modulus of equivalent block layer in concrete block pavement using finite element analysis Asish Kumar Pani, Bikasha Chandra Panda

Concrete block pavement (CBP) consists of concrete blocks of brick-sized units connected together with jointing sand and placed on a layer of bedding sand over a sub-base. The paving blocks along with the bedding and jointing sand form a composite layer called as equivalent block layer (EBL), serves the function of both wearing and base course. This paper will present the methodology to work out the elastic modulus of EBL through back calculation process using experimental deflections and finite element analysis. Finally, the mean elastic modulus of 478 MP_a has been obtained for the EBL of CBP.

Enhancement of mechanical and durability behavior of recycled aggregate concrete by accelerated carbonation and incorporation of colloidal nano-silica Manzoor Ahmad Tantray

Annually a significant volume of concrete is produced around the world as a result of the destruction of older buildings for industrialization and urbanisation or sometimes as a result of a natural disaster like an earthquake. There are a tonne of recovered coarse aggregates in this debris that is dumped in landfills. Over the time significant work has been done to validate whether recycled concrete materials can be used as replacement of constituents of concrete. In this context the present paper has mainly focused on improving the properties of recycled aggregates by the technique of accelerated carbonation and incorporation of colloidal nano-silica. The results posit that carbonation of recycled aggregate concrete (RAC) showed an increase of 10 % in compressive strength as compared to 100 % RAC ,which in addition to 3 % colloidal nano-silica resulted in 35.8 % increase in relation to 100 % carbonated recycled aggregate concrete (CRAC). Furthermore carbonation and addition of nano-silica showed significant increase on flexural and split tensile strength of concrete.