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.

The purpose of this study is to bring out the factors affecting labour productivity, which can have a strong influence on both time and cost of construction of precast concrete buildings in the developing world countries such as India. This paper also provides a brief discussion on some parameters affecting the functionality of precast concrete buildings. For identifying the ‘wastes’ in the processes and quantifying the shortcomings in the productivity, work sampling was conducted in five precast concrete construction (PCC) projects in India. Freewheeling, on-site interviews were conducted at the projects to find out the factors affecting productivity. The frequency and severity of the various parameters affecting the functionality of precast concrete buildings were obtained through a questionnaire survey. The work sampling analysis found that about 46% were NVA (Non-value adding) and NVAR (Non-value adding but required) activities, which adversely affected the productivity and that the process ‘wastes’ identified at erection sites were more than those in the production yards. The questionnaire survey on functionality revealed that ‘non-conformance with tolerance limits for precast concrete elements’ has ‘high’ frequency of occurrence and ‘very high’ severity and a field study found that about 40% of the precast panels failed to comply with tolerance limits. The reasons for ‘wastes’ in different trades viz. concreting, shuttering, reinforcement and erection in Indian PCC projects were analyzed in this paper which could help in understanding the reasons behind the prevailing low productivity. More importantly, this study also explores the parameters affecting the functionality of precast concrete buildings. While the functionality issues identified may or may not be typical of the entire precasting industry, the wastage issues identified have been widely reported in literature as quite prevalent in the construction industry.

The overall service life of concrete structures can be divided into corrosion initiation and corrosion propagation phases. Although the corrosion propagation period (tp) is usually found to be smaller than the initiation period (ti) it is important to estimate tp for planning and budgeting for the repair activities. The tp depends on the corrosion rate (icorr) of the steel reinforcement. India has many old concrete structures built using the Cold Twisted Deformed (CTD) steel bars. Now-a-days, CTD steel (being highly vulnerable to corrosion) is rarely used and the Thermo-Mechanically Treated (TMT) or Quenched and Self-Tempered (QST) steel bars are extensively used. Quantitative information on icorr of the CTD and TMT/QST bars are required for estimating tp. However, very limited quantitative information is available on icorr to estimate tp. Therefore, the current practice is to assume that the icorr of both CTD and TMT/QST steels are equal to that of plain mild steel, which might result in unrealistic estimations. This paper provides icorr data obtained from 20-month long experimental program. The icorr data were obtained using linear polarization resistance (LPR) tests on CTD and TMT/QST steel bars embedded in mortar. Twenty-five specimens were cast, cured, and subjected to a cyclic wet-dry exposure using 3.5 % sodium chloride solution. It is observed that the icorr of CTD and TMT/QST steel bars can be represented as ∼3PLN(σ, μ, γ); with ∼3PLN(0.3, 3.9, -24) μA/cm2 and ∼3PLN(0.2, 3.6, -20) μA/cm2, respectively. This corresponds to an average icorr of 26.6 and 16.7 μA/cm2, respectively, for CTD and TMT/QST steels. It is also found that, in general, icorr of TMT/QST steel exhibits less scatter than CTD steel. This paper also provides the probabilistic estimations on tp using the measured icorr data and the tp model developed by Wang and Zhao (1993). Based on the estimations, it can be concluded that the median time-to-crack for a system with CTD steel can be approximately 1.8 times less than that of a system with TMT/QST steel - indicating that early notification is required for engineers to prepare an optimized repair strategy for deteriorating structures.

Housing crisis is one of the major issues the world is facing today. Worldwide, about 330 million households in urban areas are at substandard levels. In developing countries, about 200 million households are located in slum areas. By 2025, at least 1.6 billion citizens in the world are expected to be lacking adequate housing. India, a developing country, is also facing a huge housing demand of more than 60 million (6 crores) housing units. By 2022, this is expected to reach 110 million (11 Crores). The Cast In-situ Construction (CIC) technology cannot meet this huge demand at the fast pace required. In the past, some of the developed countries have successfully met similar huge housing demands by adopting the Precast Concrete Construction (PCC) technology. This paper reviews the promotional policies for PCC adopted in select developing countries and the impact of PCC in these countries. This paper also brings out various issues hindering the growth of PCC in India based on interviews with different stakeholders. Also, an attempt has been made to identify the current promotional policies in India and the areas of potential improvement for promoting PCC in India.

Curing plays a vital role in enhancing the impenetrability of cover concrete, which is essential to ensure the desired service life of a concrete structure. However, their performance in the field is most often evaluated by compressive strength instead of durability parameters. This paper presents an investigation of the suitability of durability index tests in evaluating the performance of various field curing methods. Five reinforced concrete slab specimens were cured in the field using the following curing methods: 7-day wet hessian, three types of curing compounds, and air curing. The field-cured concrete was tested at the age of 28 days using oxygen permeability index, water sorptivity index, rapid chloride migration test, and surface resistivity. In this study, durability index tests were able to differentiate between wet and air curing. The results of this study indicate that compressive strength as a standalone criterion is not adequate for assessing the performance of field curing methods.

This paper presents a summary of the major findings from the studies conducted at Indian Institute of Technology (IIT), Madras on Limestone Calcined Clay Cement (LC3), in comparison with plain portland cement and fly ash-based binder. The study attempts to delineate the chemical and physical effects of binder components in LC3 on hydration and hardening, property development, binder chemistry and durability indicators to evolve fundamental understanding on the performance of such low clinker binders. Such an assessment can drive the practical adoption and extend the applicability of such binders in various domains of cement-based materials. The experimental strategy involved the assessment of the pore structure evolution and electrical properties on cementitious pastes, along with measurement of the durability parameters on concrete for resistance to ingress of moisture by absorption, and chloride ions by migration and diffusion mechanisms. The synergistic interactions of the blend of calcined clay and limestone impact the physical structure positively at early ages as opposed to fly ash systems, which require prolonged curing to realise their potential. The study reveals a combination of calcined clay and limestone can be a potential combination for producing high-performance concrete, more specifically in a chloride laden environment, along with the beneficial alternative resource utilisation and sustainability prospects.

Carbonation induced corrosion of the embedded stee reinforcement is a major deterioration mechanism of reinforced concrete structures, mainly in inland / highway environments of tropical countries. Carbonation leads to uniform reduction in the cross sectional area of steel reinforcement. In general, Supplementary Cementitious Materials (SCMs) can increase durability of concrete. The current study evaluates the influence of three SCMs such as Ground Granulated Blast Furnace Slag (Slag), Class F fly ash and Class C fly ash on the carbonation of concrete, assessed by both macroscopic and micro-analytica investigations. The macroscopic behaviour of concrete was assessed using accelerated carbonation and natura carbonation tests. The micro-analytical studies were conducted to understand the alteration in the micro structure of concrete with SCMs under carbonation exposure. These tests include Scanning Electron Microscopy (SEM), X - Ray Diffraction (XRD) and Thermo Gravimetric / Differential Scanning Calorimetry (TG/ DSC). The results showed that depth of carbonation is more for concretes with SCMs. However, at lower replacement levels, the difference as compared to OPC is not much significant in the case of Slag and Class C fly ash. A relationship between natural carbonation and accelerated carbonation depth was proposed based on CO2 concentration and climatic influence (tropical regions). The microstructural modifications of the paste matrix due to carbonation are explained in terms of calcite formation, decalcification of CSH and change in porosity level.

Use of supplementary cementitious materials (SCMs) has substantially increased in the construction industry in recent years. Long-term data on the effect of different SCMs on shrinkage and creep are scarce. Also, the appropriate prediction of shrinkage is important to ensure that the design can address the structural requirements when blended concrete systems are used. Towards this, an elaborate experimental programme and application of shrinkage prediction models have been performed on typical blended concretes used in India. The study involved concrete mixes with water to binder ratios (w/b) varying from 0.50 to 0.65, and binary and ternary blended binder contents varying from 280 kg/m3 to 340 kg/m3, having slag and fly ash as partial replacement of cement. The results show that the addition of fly ash and slag does not influence the drying shrinkage strain evolution significantly in comparison with the conventional concrete with same w/b and binder content. Also, it is seen that there could be considerable differences between the shrinkage strains determined experimentally and those predicted by models considered in this study.

This paper aims to adjust the model parameters of the B4 and B4s models using newly collected laboratory data for blended cement concrete systems of strength grades 25 MPa and 65 MPa. Based on the data, regression analysis for the B4s model has been performed to capture the shrinkage response at later ages better. Also, suitable adjustment of the model parameters for aggregate type and the composition of the binder was carried out. After the adjustment, the model seems to be yield improved predictions for the data set.