In-place Concrete Strength Research Articles

Assessment of Compressive Strength of Concrete Using the CAPO Test

The CAPO-Test or the Cut and Pull-Out test, also known as the pull-out test, is gaining popularity as a method for estimating the compressive strength of existing concrete structures due to its reliability, less structural damage compared to core collection, and quick in-place strength. The manufacturer of the pull-out machine has provided a general correlation for assessing the in-place concrete strength of stone chip-based concrete. Many of the concrete buildings in Bangladesh are made of brick chip-based concrete. In a few projects in Bangladesh, the CAPO test has been used to assess the concrete strength of existing structures. However, the reliability of this test for concrete made of brick chips has yet to be investigated. 20 columns from five distinct structures, which varied in age from 14 to 45 years at the time of testing, underwent the CAPO and core tests for this study. Based on the fundamental findings of this investigation, a general correlation has been established regarding concrete composed of brick chips. According to the findings, the CAPO-Test f or concrete with brick chips shows estimated strengths using the proposed correlation varies between 0% and 30% of the core strength. No prior research has been identified on evaluating the concrete strength of existing structures containing brick chips using the CAPO test; therefore, this study supports the CAPO-Test's reliability in conducting in-situ concrete strength assessments of brick chip-based structures. Journal of Engineering Science 15(1), 2024, 1-10

Lok-Test and Capo-Test pullout for in-situ concrete strength

Among the test systems for in-place concrete strength available today, two measure the in-place physical strength, pullout, and cores. Both systems are dealt with in detail in this paper, the pullout systems named LOK-TEST/CAPO-TEST (ASTM C900-19) and coring (ASTM C42/42M-18). Testing in-situ with accurate test systems will reveal effects on the final strength from a potential mix’s over transportation, pumping, consolidation, compaction, and curing. With the LOK-TEST system testing of the pre-installed inserts takes 4–5 minutes each, easily and with only one small suitcase brought along. The CAPO-TEST, originally designed to supplement the LOK-TEST, takes 15–20 minutes for each test to be performed anywhere on a structure without pre-installed inserts. No large holes are left in the structure from coring and thinner elements may be tested without weakening them structurally. The pullout test provides accurately the In-Place Strength without testing cores and the duration is about 15 minutes compared to 3–4 days for coring correctly cured. General robust correlations to strength of standard specimens exist no matter what parameter is considered for normal concrete, even for carbonation of the surface layer. With the systems the cover layer protecting the reinforcement may be checked efficiently and quickly, not at least in areas with dense reinforcement or on slim structures. Bad curing conditions are revealed and the consequences in terms of reduced service life for presence of chlorides or carbonation may be estimated swiftly. This paper is benchmarking 50 years of successful in-situ concrete strength measurements, from studies of the failure mechanism and laboratory/on-site correlations to full scale testing of structures in Europe, Scandinavia, and Canada. Six testing cases with emphasis on pullout and cores are illustrating different applications: Case 1. Production testing at the Great Belt Link, Denmark. Case 2. Service life of bridge pier, Great Belt Link, Denmark. Case 3. Curing of the cover layer evaluated by pullout and conductivity, Denmark. Case 4. Strength testing with CAPO-TEST for further loading of old bridges, Poland. Case 5. In-Situ compressive strength testing of quarantined precast concrete tunnel lining segments using CAPO-TEST, UK. Case 6. Safe and early loading with LOK-TEST, Canada. Other cases are given on www.NDTitans.com

Modified post-installed adhesive anchorage test: Investigation of in-place compressive strength of concrete and influential factors

This paper presents the Modified Post-installed Adhesive Anchorage test (MPAA) as a method for evaluating the in-place compressive strength of concrete. It considers various influential factors, including test surface characteristics, concrete strength, anchorage depth, bolt diameter, and rebar location. Additionally, a formula for calculating concrete compressive strength, applicable to various influencing factors, was suggested. The findings demonstrate the effectiveness of MPAA in assessing in-place compressive strength of concrete with a high degree of precision. Following pull-out test, the prevalent failure modes observed were vertebral failure and vertebral-bond composite failure. Moreover, diverse concrete strengths, anchorage depths, and rebar locations demonstrated differing impacts on failure modes, while test surface characteristics and bolt diameter exerted less noticeable effects. The pull-out force-displacement curve during pull-out displayed three discernible phases: the elastic phase, crack propagation phase, and descent phase. When conducting on-site assessments, it is advisable to situate test points on the side surfaces of the members. Furthermore, factors like cover thickness and rebar location should be thoroughly evaluated when positioning test points. This encompasses the prudent choice of anchorage depth and bolt diameter to improve test precision. The suggested formula for calculating compressive strength exhibited minimal error and is applicable in determining concrete compressive strength for a wide range of practical engineering contexts. This study not only establishes a theoretical underpinning and offers support for standard revisions but also furnishes valuable guidance for conducting on-site testing procedures.

Multivariate Regression and Variance in Concrete Curing Methods: Strength Prediction with Experiments

Because concrete strengths and quality are affected by various factors, multivariate regression models are often used to analyze the differences between predicted and target outputs. However, the variableness of a predicted output and how individual input parameters affect prediction reliabilities are still uncertain in practical applications, especially for the prediction of compressive strengths of concrete. This study aims to develop multivariate models for predicting concrete strengths and providing the variance analysis of prediction results by comparisons with experiment outcomes. First, this paper provides an in-depth examination of established variance analysis methods in the context of commonly used multivariate regression models. Then, based on Gaussian process regression, this study melds principal component analysis (PCA), linear discriminant analysis (LDA), and multivariate analysis of variance (MANOVA) to assess the variability in concrete strength prediction using different curing methods. This innovative approach proves effective in evaluating the precision of the correlation and regression models (R-squared values ≥ 0.9049). The comparison between prediction results and experiment outcomes shows that retaining heat in cylinders can make them become too hot and overestimate in-place concrete strength. This study improves the methodologies of regression modeling for variance analysis and improves the reliability of concrete strength prediction. Additionally, the outcomes of this research can help save a substantial amount of financial resources and time that are required to obtain experimental data on the strengths of concrete components.

A new quality measure for acceptance and payment with a QC/QA performance specification using Bayesian updating

PurposeThis paper introduces a novel quality measure, the percent-within-distribution, or PWD, for acceptance and payment in a quality control/quality assurance (QC/QA) performance specification (PS).Design/methodology/approachThe new quality measure takes any sample size or distribution and uses a Bayesian updating process to re-estimate parameters of a design distribution as sample observations are fed through the algorithm. This methodology can be employed in a wide range of applications, but the authors demonstrate the use of the measure for a QC/QA PS with upper and lower bounds on 28-day compressive strength of in-place concrete for bridge decks.FindingsThe authors demonstrate the use of this new quality measure to illustrate how it addresses the shortcomings of the percent-within-limits (PWL), which is the current industry standard quality measure. The authors then use the PWD to develop initial pay factors through simulation regimes. The PWD is shown to function better than the PWL with realistic sample lots simulated to represent a variety of industry responses to a new QC/QA PS.Originality/valueThe analytical contribution of this work is the introduction of the new quality measure. However, the practical and managerial contributions of this work are of equal significance.

Destructive and non-destructive tests on columns and cube specimens made with the same concrete mix

This research work presents the results of an experimental campaign performed on column specimens to investigate the capacity of destructive coring test and non-destructive tests to predict the in-place concrete strength. The considered non-destructive tests are Surface Hardness (SH) and Ultrasonic Pulse Velocity (UPV) ones. Using these tests’ results also SonReb method is applied. The peculiarity of this research is that the results of all the performed test on the columns are compared to results obtained from cube specimens made with the same concrete of the columns. The non-destructive predictive methods are performed on both column and cube specimens during the curing of the concrete at different ages, while the destructive coring test on columns specimens at 28th day after casting. A discussion on the comparison between drilled cores’ strength, determined using provisions of different building codes, and cube specimens’ strength is provided. In particular, the code providing the safest concrete strength predictions is identified.

Maturity method to estimate early age concrete strength in cold weather: alternative activation energy calibration

ABSTRACT Many critical concreting activities require the determination of the in-place concrete strength. It can be costly to wait too long to execute these activities, but acting too early can have a negative impact on structural performance. Conventional moulded concrete cylinders and alternative strength assessment methods such as the maturity method are commonly used to assess concrete’s in-place strength. This study is focused on a special case when the maturity method is applied for evaluating concrete strength in cold weather at an early age. Specifically, the study proposes an alternative method for calibrating the activation energy, an input for the maturity method. Concretes cured at two different temperatures are used to calibrate the activation energy. The maturity method based on this activation energy predicted the cold weather concrete’s compressive strength satisfactorily. It was also found that for a successful application of the proposed activation energy calibration, the two temperatures should represent the expected minimum and maximum temperature at the site. Furthermore, the results showed that the maturity method based on the proposed activation energy calibration method performed better than the conventional cylinder method.

4-Channel Concrete Temperature Data Acquisition System Using GPRS data Network

Objectives: To design a non-destructive, low-effort, low-cost device that can estimate the early age and compressive strength of in-place concrete in real time. The maturity protocol eliminates the need for on-site concrete cylinder break checks or hammer tapping test saving time and resources. Methods: Four different temperature sensors were used to measure the temperature of concrete in order to improve the system’s accuracy. As concrete structure monitoring with temperature sensors is a continuous process, the study includes automated data logging at regular intervals, storage of measured temperature data over time on an attached SD card, and transmission to a server through the SIM800L’s GPRS capability. Findings: The current work presents a low-cost (31 USD), low-powered (3.7v/2.8A), and portable temperature sensor and logger that will track and record temperature values so that values can be monitored remotely from anywhere on the planet. Data can be managed and tracked from any location and on any computer that has internet access. Communication between presented units with MQTT platform has been studied. Novelty/Applications: This device is a simple batteryoperated, small-size, compact, low-power data acquisition system with multiple sensors. With the support of GPRS, data can be sent to a server. Concrete testing delays are no longer a concern. It is possible to check the status of pour and receive updates anytime, wherever, on any computer with this method’s real-time data and 24/7 remote monitoring capabilities. This simple,trouble-free module is completely integrated and needs no wires or testing laboratories, allowing for quick onsite decisions and preventing unnecessary setbacks. Keywords: GPRS; DS18B20; ESP8266; MQTT (Message Queuing Telemetry Transport)

In Situ Strength Assessment of Concrete Using Recycled Aggregates by Means of Small Diameter Cores

By increasing the demolition of old concrete structures and the interest of civil industries to consume cheaper materials, using Recycled Concrete Aggregate (RCA) can cause environmental protection and decrease the construction costs. On the other hand, the high potential of Recycled Aggregate Concrete (RAC) in concrete industry was established by extensive experimental researches were performed to examine the properties of RAC. Like in conventional concrete, core test cut from RAC can be used to assess the in-place concrete compressive strength and sometimes it becomes an important test for monitoring in-situ properties of concrete to taking up retrofitting/strengthening measures. So the core test is often mentioned in most codes for concrete testing. The layout of this study includes four concrete mixes, two concrete grades (20 and 40 MPa), three core diameters (46, 69, and 100 mm), five length-to-diameter (L/D) ratios (1, 1.25, 1.5, 1.75, and 2), two sizes of maximum coarse recycled aggregates (10 and 20 mm), two directions of core drilling which are vertical and horizontal and three ages of specimen (14, 28 and 90 days). The core test results were compared to cylindrical and cube specimens. Results imply that the core strength of recycled concrete reduces with the increase in aspect ratio, by decreasing the core diameter, increasing the size of coarse aggregates in recycled concrete. By analyzing the results a comparison was made between recycled concrete in this study and conventional concrete in other studies, as well as code instructions.

Relationships between compressive and flexural strengths of concrete based on fresh field properties

Premature cracks are attributed to traffic-induced stresses, weather, and construction deficiencies, resulting in durability cracking, spalling, and popouts. These distresses can cause many problems, such as frequent maintenance, increased vehicle repair costs and safety concerns. Furthermore, poor road conditions can lead to vehicle crashes, which can cost billions of dollars annually and cause fatalities. Efficiently determining the strength of in-place concrete is therefore crucial for traffic safety and quality assurance. This study analyzes the fresh field properties (unit weight, air content, slump, and temperature), compressive, and flexural strengths of 1,342 concrete specimens to determine models that correlate the compressive and flexural strengths for normal strength concrete. The root mean square error was used to analyze the accuracy between the values predicted by the models and the laboratory values. Existing models reported by researchers were analyzed using the same method and compared to the proposed models developed in this study. Based on the analysis, a positive nonlinear correlation between the compressive strength and flexural strength of normal strength concrete was determined. The air content was found to be the most significant fresh field property and has a negative correlation with both the compressive and flexural strengths. The proposed regression equations exhibit small errors when compared to the experimental results, which allow for efficient and accurate predictions of the flexural strength.

In-Place Estimation of Concrete Compressive Strength Using Postinstalled Pullout Test – A Case Study

Abstract It was proposed that a 16-story steel framing structure be built on top of an existing 12-year-old 1-story reinforced-concrete structure. The in-place concrete compressive strength of 3 footings and 29 plinths was estimated using a postinstalled pullout test and a core compressive strength test. The influence of different length-to-diameter ratios of the cores and different diameters of cores and the correlation between maximum pullout force and core compressive strength were investigated. The results of the pullout test and core strength test indicate that the concrete compressive strength of footings and plinths was considered structurally adequate as per the acceptance criteria for tested core strength and estimated core strength given by ACI 318, Building Code Requirements for Structural Concrete and Commentary, and ACI 228.1R, In-Place Methods to Estimate Concrete Strength, respectively. Maximum pullout force had a strong correlation with the core compressive strength. The influence of the different length-to-diameter ratio of cores on the strength correlation was not significant if the raw results of the compressive strength tests were corrected by multiplying the corresponding correction factors for the length-to-diameter ratio given by ASTM C42, Standard Test Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete. The mixed use of the test results of 3.20 and 3.74-in. (81-mm and 95-mm) cores resulted in a decrease in the R2 of the correlation model, compared to that of the correlation model based on 3.74-in. (95-mm) cores. This was attributed to the potentially increased testing error as the diameter of the cores decreased. Recommendations for successfully performing postinstalled pullout tests in the field were proposed. With the use of pullout tests, the project team was able to determine that the existing structural members had sufficient capacity. A delay in the project schedule was avoided.

Prototyping an embedded wireless sensor for monitoring reinforced concrete structures

Current article proposes a cheap prototype of an embedded wireless sensor to monitor concrete structures. The prototype can measure temperature and relative humidity concurrently at a controlled through smartphone time interval. It implements a maturity method to estimate in-place concrete strength, which is considered as an alternative for traditional shock impulse method and compression tests used in Kazakhstan. The prototype was tested and adequately performed in the laboratory and field conditions. Tests aimed to study the effect of internal and ambient temperature and relative humidity on the concrete strength gain. According to test results revealed that all parameters influence the strength gain to some extent. For a better understanding of how strongly parameters influence the strength as well as each other, proposed a multicolored cross-correlation matrix technique. The technique is based on the determination coefficients. It is able to show the value of significance of correlation, its positivity or negativity, as well as the degree of inter-influence of parameters. The prototype testing also recognized the inconvenience of Bluetooth control due to weakness of signal and inability to access several prototypes simultaneously. Therefore, further improvement of the prototype presume to include the replacement of Bluetooth by Narrow Band IoT standard.

Maturity curve for estimating the in-place strength of high performance concrete

The paper presents the maturity curve for estimating the in-place early-age compressive strength of concrete. The development of appropriate maturity curve is a complex process. It is important to correctly determine the datum temperature and activation energy, which can be obtained in mortar tests. This paper describes an investigation of the accuracy of the maturity method to estimate the strength when different way to rate constant and maturity function are analysed. High performance concrete used for construction of extradosed bridge was tested. The developed curve was implemented to predict the concrete strength at three construction stages, in summer, autumn and early spring.

Experimental assessment of concrete compressive strength in old existing RC buildings: A possible way to reduce the dispersion of DT results

Reliable appraisal of the in situ compressive strength is a key challenge in the seismic assessment of existing RC structures, due to its high variability throughout them and because it often represents the most important strength parameter adopted in the structural analyses. For this reason, in this paper a procedure to obtain a more accurate concrete strength characterization is proposed and applied to several case studies. The method provides a reduction of test results’ variability by taking into account the influence of casting operations on it and may support existing codes for a correct in-place concrete strength evaluation.

Behavior of recycled aggregate concrete-filled basalt and carbon FRP tubes

This paper presents the results of an experimental study on the axial compressive behavior of concrete-filled FRP tubes (CFFTs), prepared using different amounts of recycled concrete aggregate (RCA). Thirty-six CFFTs were tested under axial compression. The effects of the RCA replacement ratio, specimen cross-sectional shape, FRP type, and concrete strength were studied. The results suggest that the axial stress–strain behavior of CFFTs is affected by the amount of RCA, which particularly affects the ultimate axial strain and FRP hoop rupture strain. For a given in-place concrete strength, an increase in RCA content leads to a decrease in compressive strength and an increase in ultimate axial strain of FRP-confined concrete. The results also indicate that the increased RCA content leads to a decrease in the hoop rupture strain of CFFTs. CFFTs manufactured with carbon FRP tubes instead of basalt FRP tubes and CFFTs with circular cross-sections instead of square cross-sections develop a higher compressive strength and lower ultimate axial strain. The effects of specimen cross-sectional shape and FRP type on the axial compressive behavior of CFFTs vary with RCA content.

Use of maturity method to estimate compressive strength of mass concrete

In this study, maturity method was used to estimate in-place strength of large concrete placements. Four 6-foot (1.8m) cube concrete blocks were constructed in four different locations, and the strength development curves for these concrete mixtures were established using 6 by 12inch (150 by 300mm) cylinder specimens collected from the construction site. Activation energy values for the concrete mixtures were determined in the laboratory and used for equivalent age calculations. Sacrificial temperature sensors embedded throughout the depth of the concrete cubes were used to monitor temperature histories in specific locations up to 28days. Equivalent age was employed to estimate in-place concrete strength based on the collected temperature histories. Four inch (10cm) diameter core samples, with 6-foot (1.8m) in length, were taken from the cubes at 4, 28 and 56days after construction and the core strengths were compared with the predicted strengths using maturity relationships. Results show that the predicted in-place concrete strength is always higher than the actual core strength on top surface locations. Results from three different cubes show that core compressive strength from mid-section were within ±15% of the predicted values and core results from the bottom section were generally higher than the predicted values.

Maturity-Based Field Strength Predictions of Sustainable Concrete Using High-Volume Fly Ash as Supplementary Cementitious Material

The use of fly ash in concrete has received significant attention during recent years, owing to environmental concerns regarding its disposal and to its potential use as a supplementary cementitious material owing to its ability to improve concrete performance. Although a fly ash content of less than 25% of the total cementitious content is routinely used in concrete, high-volume fly ash (HVFA) concrete is not commonly used because of perceived lower early age strengths. The objective of this research was to use maturity based modeling to demonstrate that the beneficial effects of high temperatures observed in structural elements such as slabs and concrete beams during the hydration process associated with the mass features of such elements may compensate for the slower rate of strength gain of fly ash concrete that is typically observed in standard laboratory cured cylinders. Match cured cylinders were used during this process to estimate the early age in-place strength of HVFA concrete and to confirm the predicted mature strengths. The results have shown that standard and field cured cylinder strengths underestimate the in-place concrete strength. High in-place temperatures owing to the mass characteristics of structural elements result in increased and satisfactory in-place early age strengths for construction, measured by match cured cylinders and pullout testing, and predicted by maturity modeling.

On the dispersion of data collected by in situ diagnostic of the existing concrete

The compressive strength of in-place concrete is a crucial mechanical parameter which influences the performance level and the safety assessment of existing RC structures both under seismic loads and under dead loads. Italian NTC and Eurocode 8 [1,2] have established that the fundamental basis of the safety assessment is the “Knowledge Level (KL)”, which shall be defined according to the procedures adopted for in situ inspection and materials testing (destructive and non-destructive). Within this framework – in the case of RC constructions – a major requirement is the explicit identification of the reference values for the strength of in situ concrete. The afore mentioned building codes, however, do not include any consideration about the uncertainty level affecting the results of in situ tests, which can indeed invalidate the reliability of the mechanical parameters. This problem is instead well addressed by FEMA 356 [3], which prescribes a limit value (14%) to the statistical dispersion of the measures performed on a set of concrete specimens. In this paper, after presenting and discussing a procedure applied for processing experimental data provided by in situ tests in a number of real case studies (school buildings in the Province of Foggia, Italy), the attention will be focused on the problem of the data scattering in the case of in situ concrete strength. It is shown that the variance is a crucial parameter, which should always be considered when performing the safety assessment, even if FEMA requirements, in this respect, are too much restrictive.

A Nondestructive Testing Technique: Nail Penetration Test

This study presents a practical nondestructive testing (NDT) method: the nail penetration test (NPT). The major tools of the test technique are a gas nailer with 130 J (95.88 ft-lbf) power, concrete nails, and a gas nailer cell. The study covers three different limestone aggregate types. Six concrete mixtures were prepared from each aggregate type. Five nail shots were performed on each concrete mixture (or grade) and the average value was obtained. The average nail penetration depths were correlated with the compressive strength of concrete. Other NDT techniques, such as the Schmidt rebound hammer (SRH), ultrasonic pulse velocity (UPV), and Windsor probe (WP), were also applied to concrete samples. The measured compressive strength values were compared with those obtained from the empirical relationships using the data from the NPT, SRH, UPV, and WP. It was found that the reliability of the NPT to estimate the compressive strength of concrete is very high. The tool employed in the investigation covers a relatively wide range of compressive strength of concrete. This testing tool is proposed to estimate the compressive strength of in-place concrete.

Effect of Chemical Admixtures on Apparent Activation Energy of Cementitious Systems

The Arrhenius equation is often used to characterize the progress of portland cement hydration for predicting in-place concrete temperature, strength, and other properties. To apply the Arrhenius equation, an activation energy (Ea) value representing the temperature sensitivity of the hydration reactions must be determined. The effects of concrete mixture variables on activation energy, including the effects of chemical admixtures, have not been well researched. This paper examines the effects of set-accelerating, water-reducing/set-retarding, and air-entraining admixtures on apparent (i.e., experimentally determined) activation energy for mixtures with and without supplementary cementitious materials. It was found that a glucose-based water-reducing retarder and two high-range water-reducing admixtures slightly lowered Ea, a lignosulfonate-based water-reducing retarder and a calcium nitrate–based set-accelerating admixture significantly lowered Ea, and a vinsol resin air-entraining agent had no effect.