Prototyping of a concrete maturity sensor with a hermetically sealed housing made of two-component plastic

The construction industry, traditionally considered quite conservative, is now going through a marked change. With competition intensifying, companies have begun to gradually adopt various digital technologies to reduce construction costs, such as the wireless concrete monitoring sensors, which implement a temperature-strength monitoring method for concrete. Each device has its technological features, which are considered in the development of the concepts. Enclosure design is the most important stage of product development. An enclosure made in-house has many advantages and disadvantages. The most important part of the design of an electronic device enclosure is the preliminary research stage. This article presents features of wireless monitoring sensor enclosure design. A data acquisition station (DAS), also referred to in the network topology as a “gateway”, will be used to collect data from the wireless monitoring sensor over the selected protocol. The server application was created based on HTML, PHP, CSS, JavaScript. Testing of the wireless monitoring sensor, SDS, and the server application working together showed full functionality. A study is also given on the determination of concrete strength using the developed sensor according to the ASTM method and using the IPS MG 4.0 by GOST.

APPLICATION FEATURES OF CONCRETE STRENGTH MONITORING SENSORS

The paper presents an algorithm of application of concrete strength monitoring sensors taking into account such features as a selection of sensor type, selection of concrete mixture calibration method according to regulated requirements, consideration of concrete maturity sensor location, degree of influence of hardening temperature on strength gain based on isotherms construction. This algorithm was reflected in practice, as the wireless sensor for concrete strength monitoring developed within the project was applied according to the selected scheme in real-time.

The Effects of Steam-Curing on the Properties of Concrete

Worldwide, concrete is the most preferred construction material. The steam curing method is favored when there is a need for accelerating strength. This paper presents the study of the compressive and flexural tensile strength of concrete subjected to eight different steam cures. In addition, the stress-strain curve and the modulus of elasticity were determined at the age of 28 days. The compressive strength test results show that after treatment, strength increases with concrete maturity. A cycle with a pre-heating period gives better results than a cycle without a pre-heating period. The longer the duration of the maximum temperature period, the lower the strength drop compared to the control concrete. The best results were obtained for concrete treated according to the following cycle: a 3-hour pre-heating period at 20oC, a 2-hour increase of temperature from 20 to 70oC, and a 3 hour of maximum temperature of 70oC.

Rebound Hammer Test: An Investigation into Its Reliability in Applications on Concrete Structures

The issue of concrete strength often arises in civil engineering practice, either due to quality control of new constructions or due to the assessment of existing structures. To this aim, one of the most widely spread techniques is the rebound hammer (Schmidt hammer) test, for which calibration is still related to the original Schmidt curve dating back to the early 50’s. In spite of the large amount of research work performed in the last decades, the uncertainties of the rebound test are still not clearly quantified and open to further insight. This paper presents and discusses a wide research campaign on laboratory specimens and on third-party specimens delivered to the Laboratory for Building Materials of the University of Genoa, Italy, for standard quality controls. While it is well known that moisture content, surface finishing, and concrete maturity strongly affect the test result, the effect of the stress state has not yet been studied and is found in this research to be a further parameter affecting the test reliability. The final outcome of all the uncertainties is variability in estimated concrete strength as large as ±70%; additionally, some issues are discussed on the intrinsic uncertainty of this test. As already demonstrated by many authors, the results of this research also show that a universal calibration curve to be used for any concrete, in any condition, conceptually does not exist.

Activation Energy for the Concrete Maturity Model – Part 1: Compressive Strength Tests at Different Curing Temperatures

The article addresses the modelling of the maturity of concrete. The apparent activation energy is the backbone of the Arrhenius model, which is typically used to model the maturity of concrete. The maturity (or the equivalent age) is influenced by the curing temperature and it is applied when modelling the hydration process and the hardening of concrete for instance in order to forecast the early-age strength to determine the time for removal of formwork or the time for prestressing. Part 1 of the article describes the background for the maturity model and the test series carried out at the DTI concrete lab.Laboratory tests at different curing temperatures (from 5°C to 60°C) are presented and the compressive strength results are modelled according to the original Freiesleben Hansen and Pedersen maturity model that has been applied in the field for many years. The tests include five different concretes, using three different cement types and the addition of fly ash. There are significant differences especially when considering the later-age strength modelling at either low temperatures or at high temperature curing.

Activation Energy for the Concrete Maturity Model – Part 2: New Model for Temperature Dependent Ea

The article addresses the modelling of the maturity of concrete. The apparent activation energy is the backbone of the Arrhenius model, which is typically used to model the maturity of concrete. The maturity (or the equivalent age) is influenced by the curing temperature and it is applied when modelling the hydration process and the hardening of concrete for instance in order to forecast the early-age strength to determine the time for removal of formwork or the time for prestressing. Part 1 of the article describes the background for the maturity model and the tests carried out as part of a large test programme at the DTI concrete lab. The tests were applying iso-thermal curing temperatures from 5°C to 60°C for various durations before measuring the compressive strength.Part 2 of the article presents a model for the activation energy based on these test results. An alternative formulation of the maturity model is suggested and compared with other similar concrete tests found in the literature for early-age strengths. The alternative model is shown to give better accuracy when modelling the early-age strengths of concrete. The tests include five different concretes, using three different cement types and the addition of fly ash.

Concrete Construction: How to Explore Environmental and Economic Sustainability in Cold Climates

In many cold regions around the world, such as northern China and the Nordic countries, on-site concrete is often cured in cold weather conditions. To protect the concrete from freezing or excessively long maturation during the hardening process, contractors use curing measures. Different types of curing measures have different effects on construction duration, cost, and greenhouse gas emissions. Thus, to maximize their sustainability and financial benefits, contractors need to select the appropriate curing measures against different weather conditions. However, there is still a lack of efficient decision support tools for selecting the optimal curing measures, considering the temperature conditions and effects on construction performance. Therefore, the aim of this study was to develop a Modeling-Automation-Decision Support (MADS) framework and tool to help contractors select curing measures to optimize performance in terms of duration, cost, and CO2 emissions under prevailing temperatures. The developed framework combines a concrete maturity analysis (CMA) tool, a discrete event simulation (DES), and a decision support module to select the best curing measures. The CMA tool calculates the duration of concrete curing needed to reach the required strength, based on the chosen curing measures and anticipated weather conditions. The DES simulates all construction activities to provide input for the CMA and uses the CMA results to evaluate construction performance. To analyze the effectiveness of the proposed framework, a software prototype was developed and tested on a case study in Sweden. The results show that the developed framework can efficiently propose solutions that significantly reduce curing duration and CO2 emissions.

Assessing the Strength of Lightweight Concrete using Oil Palm Shells (OPS) as Coarse Aggregates

The usage of concrete spans the length of civilization and in modern day construction environment, concrete remains one of its major materials. As a result of high cost of construction and construction materials especially in Ghana and other developing countries in West Africa, different efforts have been made to find alternative local building materials to substitute wholly or partly some of the constituents of concrete. This paper looks at the potential of oil palm shells (OPS) as coarse aggregate in lightweight concrete by mainly assessing the compressive strength of OPS concrete and also establish the best mix ratio for OPS concrete. The coarse aggregate of the mix ratios 1:2:4 and 1:3:6 were replaced with OPS and their densities and compressive strengths determined on the 7th, 21st and 28th days of the concrete maturity. It was found that OPS can be used to replace coarse aggregate up to 75% in 1:2:4 mix ratio and up to 50% in 1:3:6 mix ratio. It is therefore recommended that the best mix ratios are 1:2:2:2 and 1:3:3:3. Single storey residential buildings, offices and footbridges are some of the recommended structures that OPS concrete could be suitable for. Keywords: Lightweight concrete; oil palm shell aggregates; density; concrete cubes; concrete maturity