Aaltodoc Repository :: Browsing by Author "Ojala, Teemu"

Browsing by Author "Ojala, Teemu"

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Analyzing the air-entrainment of fresh concrete with an acoustic measurement system
(2017-10-30) Ojala, Teemu; Punkki, Jouni; Insinööritieteiden korkeakoulu; Punkki, Jouni
Increased air contents have been reported from the drilled samples of finished concrete structures lately in Finland. The biggest air contents have been measured to be over 15 percent which are resulted in inadequate compressive strengths in the structures. Because it has been found that the air-entrained bubbles are very sensitive, a proper quality control for the whole supply chain in the production of concrete is highly recommended. By improving the quality control these defects could be noticed sooner, which would decrease the expenses from the follow-up repair procedures. The quality control of the concrete is mainly based on old measurement methods that are laborious and time-consuming. The digitalization of the measurement equipment would offer continuous quality control monitoring that could be integrated into automatic defect detecting systems in the future. This thesis analyses the air-entrainment of fresh concrete using an acoustic measurement system called CiDRA AIRtrac. The system allows measurements in real-time directly in a rotating mixer. The air amount measurements are based on the speed of the sounds where the increased air content leads to a slower travel time in bubbly liquids. Measuring the air amount in a mixer is effortless and fast when compared to the traditional methods that are meant for fresh concrete. On this research, the AIRtrac technology was found to measure the air amount of the fresh concrete accurately when the minimum requirements were met. The biggest factors that affected the measurement precision were the batch size and workability of the concrete. However, these limitations should not affect the measurements outside the laboratory environment where the mixers are used on higher capacity. Even though the traditional methods give more precise measurements, the integration possibilities with digital interfaces makes them applicable for future saving time and labor. In addition, the continuous measurement opens new possibilities in the development of concrete additives. By analyzing the air content continuously, the technology gives an additional information about the effects of different admixtures that could not be received using older measurement methods. Furthermore, the collected data gives a visual representation of the air development that can be used in analysis of different mixers. The effects of the mixing energy and sequences using concrete chemicals could be also analyzed.
Betonin koostumuksen vaikutus sen tiivistettävyyteen - Raportti tilaustutkimusprojektista
(Aalto University, 2019) Ojala, Teemu; Al-Neshawy, Fahim; Punkki, Jouni; Rakennustekniikan laitos; Department of Civil Engineering; Betonitekniikka; Insinööritieteiden korkeakoulu; School of Engineering
Fresh concrete may contain up to 20% of entrapped air before compaction. The amount of air depends not only on the properties of the concrete but also on the mould and the reinforcement. The purpose of compaction is to remove the entrapped air as well as possible. It is assumed that entrained air is not significantly impacted by the compaction. Lately, it has been noted that the compaction of concrete might not be always sufficient. This phenomenon has been observed in the cases where half–full-sized test structures has been cast. The density of the drilled cores has been notably lower (100...150 kg/m3) compared to the laboratory specimen used in quality control. Correspondingly, the estimated air content of the hardened concrete has been higher than the target level and the compressive strength of the concrete structure has been measured to be notably lower than in the laboratory specimen. The purpose of the contract research project "Good vibrations", carried out in Aalto University, Department of Civil Engineering, was to investigate how the composition of concrete affects the degree of compaction and how much compaction different concrete types require. The research was based on the test structures cast in the ready-mix plant. Drilled cores were extracted from the hardened test structures and their densities and compressive strengths were analyzed. In addition, the compaction in the mould was recorded from two angles. Realized vibration times and the removal of the entrapped air was estimated from the recordings. The results show that the compaction fills the mould easily but removing the entrapped air is challenging. After normal vibration times, the remaining amount of entrapped air was generally 1...4% more than in the laboratory specimen. This corresponds to a reduction of the compressive strength about 5...20%. In addition, the workability of concrete, low water-cement ratio or high superplasticizer amount seem not to have a clear effect on the degree of compaction. It was noted that vibration may easily cause segregation of the concrete. Especially, air-entrained concretes with high workability are susceptible to segregate even with short vibration times. However, with common vibration times this risk is moderately low as well as the segregation seems to have little effect on the average strength of the test structures. The sensitivity of air-entrained concrete for segregation requires further research. The practical goal of the project was to develop instructions for compacting the concrete. In this report, a four-step process was formulated where a poker vibrator is used for compaction.
Characteristics of Entrained Air Voids in Hardened Concrete with the Method of Digital Image Analysis Coupled with Schwartz-Saltykov Conversion
(MDPI AG, 2021-05-01) Ojala, Teemu; Chen, Yanjuan; Punkki, Jouni; Al-Neshawy, Fahim; Department of Civil Engineering; Mineral Based Materials and Mechanics
This paper presents the characteristics of air void systems in hardened concrete with the method of digital image analysis (DIA) coupled with Schwartz-Saltykov (SS) conversion. The results indicate that the DIA method coupled with SS conversion estimates the air content with more accuracy than it would without SS conversion; the correlation between air content obtained from the DIA method, and that from the thin section (TS) method is as good as the correlation observed between the pressure saturation (PS) method and the TS method. It was also found that the DIA method shows a better correlation with the TS method when the spacing factor without SS conversion is considered, while both methods show poor correlations when the corresponding specific surface is considered. In addition, it indicates that the peak of three-dimensional size distribution (3-DSD) of air voids after SS conversion falls in smaller voids, and 3-DSD of air voids shifts to a narrow size range, in comparison with the 2-DSD without SS conversion; the shape of the 3-DSD air voids remains constant irrespective of the class widths. Increasing the number of classes can minimise the standard deviation in the estimation, however, it also results in a leap in voids volume density, which will influence the estimation of air content.
Determination of water/cement-ratio of cement
(2018) Tauqir, Ammad; Ojala, Teemu; Insinööritieteiden korkeakoulu; Punkki, Jouni
Water/cement-ratio (w/c-ratio) is an important factor affecting quality of the concrete, which has motivated engineers to do research on determining the w/c-ratio. The traditional way to estimate the w/c-ratio by weighing the cement and water from mix design. The estimated results are usually not accurate as the other factors affect the accuracy such as moisture in the aggregates and water added in the construction site. In this thesis other methods are investigated to determine the w/c-ratio of fresh and hardened concrete. The research was carried out in the literature review which consisted of an effect of hydration process, a source of water in the concrete, workability of the concrete as well as w/c-ratio effect on the strength of the concrete. The laboratory work consisted of the preparation of nine concrete with three different w/c-ratio and each w/c-ratio is divided into three categories of air content ranging from 2% to 10% by volume. Different measurement methods are explained in the experimental part to determine the w/c-ratio of fresh and hardened concrete. Three methods are exploited to determine w/c-ratio of fresh concrete and one method for hardened concrete. The methods utilized in the fresh concrete are hydro-mix, SONO-WZ and microwave oven. The capillary suction method is used for the hardened concrete. Based on the result and calculation, Hydro-mix shows moisture content in the real-mixing time and it shows good results with higher air content. SONO-WZ is a portable measuring device it shows good results with higher w/c-ratio and concrete with the air content in the range of 2% to 7%. SONO-WZ is not a suitable device for the 9–10% air content concrete that is because the air gaps in the high air content concrete which affect the flow of dielectric current. Microwave shows reliable results, however, the results are less than the actual w/c-ratio because there is still some entrapped air left in the sample. Digitalization measurement system plays an important role in modernizing the quality control of concrete. It is beneficial to measure the workability, moisture content and air content of concrete in all phases of concrete production. These measurement technologies measure the properties of concrete in real-time with minimal effort and less supervision.
EPS-lisäeristämisen vaikutus asuinkerrostalon palovahinkoihin
(2015-04-21) Ojala, Teemu; Hostikka, Simo; Insinööritieteiden korkeakoulu; Hostikka, Simo
Estimating the Workability of Concrete with a Stereovision Camera during Mixing
(MDPI AG, 2024-07) Ojala, Teemu; Punkki, Jouni; Department of Civil Engineering; Mineral Based Materials and Mechanics
The correct workability of concrete is an essential parameter for its placement and compaction. However, an absence of automatic and transparent measurement methods to estimate the workability of concrete hinders the adaptation from laborious traditional methods such as the slump test. In this paper, we developed a machine-learning framework for estimating the slump class of concrete in the mixer using a stereovision camera. Depth data from five different slump classes was transformed into Haralick texture features to train several machine-learning classifiers. The best-performing classifier achieved a multiclass classification accuracy of 0.8179 with the XGBoost algorithm. Furthermore, we found through statistical analysis that while the denoising of depth data has little effect on the accuracy, the feature extraction of mixer blades and the choice of region of interest significantly increase the accuracy and the efficiency of the classifiers. The proposed framework shows robust results, indicating that stereovision is a competitive solution to estimate the workability of concrete during concrete production.
Evaluation of concrete frost resistance testing methods
(2024-08-19) Vesinurm, Raul; Ojala, Teemu; Iqbal, Ahsan; Insinööritieteiden korkeakoulu; Punkki, Jouni
The frost resistance of concrete depends on multiple factors, and its accurate quantification can be difficult due multiple possible methods of testing. The objective of this thesis was to survey and evaluate the most popular direct and indirect western frost resistance tests, to compare these tests with each other, and to investigate the effect of supplementary cementitious materials on them. This thesis begins by reviewing the literature on mechanisms of frost damage and the properties affecting frost resistance. Afterwards, different frost resistance testing methods are discussed. Lastly, four different cements, with varying degrees of slag, are tested at water-to-binder ratios of 0.40 and 0.45 in order to evaluate different methods of testing, and the possible influence of slag on the results. The air content was measured with the pressure gauge method and the gravimetric method from fresh concrete, and from hardened concrete with polished section analysis and the pressure saturation test. In addition, a capillary suction test, compressive strength test, and the slab test were done. The results confirmed that slag decreases the surface scaling resistance of concrete and sorptivity. The air content measurements showed loss of entrained air during hardening. A spacing factor below 0.20 mm was found insufficient in guaranteeing satisfactory surface scaling resistance, which might due to the amount of slag in the concrete samples.
Factors for compactibility and risk of segregation for concrete - Report for contract research project "Compact Air"
(Aalto University, 2021) Ojala, Teemu; Ahmed, Hassan; Vehmas, Tapio; Chen, Yanjuan; Tauqir, Ammad; Oey, Tandre; Al-Neshawy, Fahim; Leivo, Markku; Punkki, Jouni; Rakennustekniikan laitos; Department of Civil Engineering; Concrete Technology; Insinööritieteiden korkeakoulu; School of Engineering
Compaction of concrete allows the concrete to reach its full potential quality. Compaction is a two-stage process where the vibrations effect first fills the mould due to the liquefaction, and second, the vibrations repulse the entrapped air from the concrete. The purpose of the Compact Air project was to determine possibilities to reduce the amount of compaction pores and reduce the risk of segregation. Firstly, the samples from the project "Good Vibrations" were analysed using combination of capillary suction, pressure saturation, and digital image analysis methods. These three methods were also applied on normal production concrete structures, from which drilled cores where vertically extracted. Secondly, test structures were cast to examine where the compaction pores are created and how the reinforcement as well as the compaction power affect the compaction pores. Finally, a rheological model for concrete under vibration was created to further understand the factors affecting the compaction process. The experiments did not reveal any single factor to improve the compactibility nor reduce the risk of segregation. However, the results demonstrated well that the workability and compactibility are not correlated phenomena. The casting of the test structures showed that even though the fluid concrete quickly filled the mould, the required compaction time remained in the same level when compared to the stiff concrete. According to the rheological modelling, the maximum density of concrete is a parameter that is controlled by the selection of compaction time, but it can also be increased by improving concrete properties. The visual estimation and modelling of the optimal vibration time suggest that the optimal vibration cannot remove all the entrapped air. Therefore, the compaction process is always a compromise between the degree of compaction and segregation. The effects of the superplasticisers during the compaction are complex even though the superplasticiser had minor impact on the rheological properties of the concrete. Since superplasticisers increase the slump value of concrete by decreasing the yield stress, their effect on viscosity is relatively small, and thus, have little influence on the compactibility. While the vibration mechanically breaks down the cement particle interactions, the plasticisers permanently reduce those interactions of the cement particle. Due to the permanent loss of interactions, plasticised concretes are more susceptible for segregation during vibration when compared to the non-plasticised concretes. Moreover, lower viscosity of the cement paste increases the velocity of compaction pores raising upwards, reducing the required time for entrapped air to exit the concrete. The best compaction quality can be achieved with a moderate workability concrete. Importantly, the height of compaction layers, the distance of compaction points, and the compaction times affect greatly the overall compaction quality. As such, the whole compaction process has a significant impact on the quality of concrete.
Machine learning approach for estimating workability of concrete from mixing image sequences using 3D stereo camera.
(2021-10-18) Azhar, Saad; Masood Mustafa, Khalid; Ojala, Teemu; Insinööritieteiden korkeakoulu; Punkki, Jouni
Concrete is one of the most utilized man-made material on earth and therefore its properties are important to study. Workability of concrete is a property of fresh concrete that refers to how easily the concrete can be placed, consolidated, and finished. It is commonly measured using a slump test where more fluid concrete yields a higher slump. Slump can be categorized into multiple slump classes depending on its fluidity. Performing the slump test is a laborious task and prone to manual errors, hence there is a need to find measurement solutions based on modern technological advancements to estimate the workability. The aim of this thesis was to investigate the potential of depth sensor data to predict the slump classes of concrete using machine learning. The depth sensor was mounted on a mixer that recorded the mixing process of concrete. Visualizing the depth data of the mixing process revealed a sinusoidal pattern for slump classes with each having a different peak. This visualization was used to remove noisy data as well. Haralick features are 13 statistical properties such as entropy and contrast that can be extracted from an image as useful information. These properties were used to train various machine learning classifiers to learn from and then predict the slump class of a concrete mix. High classification accuracy of up to 94% was achieved demonstrating that using depth data with machine learning is effective in estimating the workability of concrete while mixing.
Monitoring of concrete segregation using AC impedance spectroscopy
(Elsevier Science Ltd., 2023-06-27) Ojala, Teemu; Ahmed, Hassan; Kuusela, Petri; Seppänen, Aku; Punkki, Jouni; Department of Civil Engineering; Mineral Based Materials and Mechanics; Department of Civil Engineering; University of Eastern Finland
Segregation is one of the major phenomena decreasing the durability of concrete and increasing its risk of failure. This paper investigates the feasibility of AC Impedance Spectroscopy (ACIS) to serve as a monitoring technique for the concrete segregation during compaction. The impedances of fresh concrete were determined between compaction intervals. Changes in the calculated bulk resistivities were compared to hardened densities of the drilled cores, as well as to aggregate segregation obtained via digital image analysis of the hardened concrete sections. During the compaction process, a significant difference in the bulk resistivity was observed between the top and bottom parts of segregated specimens in comparison to unsegregated specimens. By inspecting the relationship between the measurement methods, it was found that ACIS provides a reliable approach (r=-0.948) for estimating the segregation level in cases where the resistivity is mostly affected by the movement of aggregates.
Stability of Air Content in Fresh Concretes with PCE-Based Superplasticizers
(NORDIC CONCRETE FEDERAT, 2019-07) Al-Neshawy, Fahim; Ojala, Teemu; Punkki, Jouni; Mineral Based Materials and Mechanics; Department of Civil Engineering
Air contents of concrete are necessary for concrete durability in freeze-thaw exposure. According to the Finnish concrete code, the target value for air content varies between 4% and 5.5% for XF -exposure classes. Lately in Finland, some cases showed an elevation of air contents up to 15% in fresh air-entrained concrete at construction site and in drilled concrete samples. The objectives of this study were to investigate the stability of air entrainment by measuring the air content elevation 30 minutes and 60 minutes after concrete mixing and investigating the concrete sensitivity to segregation. Composition of concretes used in this study include 7 different combination of PCE based superplasticizer and air-entraining agent admixtures, cement content of 425 kg/m(3), two consistency classes S3 with water to cement ration of 0.33 and F5 with water to cement ration of 0.38. One cement type was used for all concrete mixes. The concretes were mixed for 2 minutes and 5 minutes mixing times. The results show thatthe elevation of the air content of fresh concrete depends on the consistency of the concrete and on the used combination of superplasticizer and air-entraining agents. The higher consistency classes concretes have more risk of air elevation with some combinations of PCE-based superplasticizers and air-entraining agents. The results also indicate that short mixing time would not be enough to achieve total effectivity of some air-entraining agents, especially for higher consistency classes concrete.
Suoratoimitus verkkokaupan liiketoimintamallina
(2024-08-27) Ojala, Teemu; Wallenius, Hannele; Perustieteiden korkeakoulu; Rajala, Risto
Verkkokauppa on kehittynyt merkittävästi viime vuosikymmeninä, siirtyen postimyynnistä monimuotoisiin digitaalisiin alustoihin, jotka mahdollistavat tuotteiden ja palveluiden nopean sekä joustavan maailmanlaajuisen kaupan. COVID-19-pandemian seurauksena siirtymä fyysisistä vähittäiskaupoista verkkokauppoihin on kiihtynyt entisestään. Globaali pandemia sai verkkokaupat sopeutumaan äkillisesti muuttuviin olosuhteisiin ja etsimään joustavampia liiketoimintamalleja, joiden avulla verkkokaupat selviytyisivät kriisitilanteista tulevaisuudessa paremmin. Tässä kandidaatintyössä tutkitaan suosioon noussutta suoratoimitusmallia, jossa verkkokauppias ei itse pidä varastoa eikä omista myymiään tuotteita, vaan verkkokaupan tuotteet lähetetään jakelijan varastolta suoraan asiakkaalle. Tämän kandidaatintyön tavoitteena on tunnistaa suoratoimituksen keskeisimmät edut ja haasteet, keskittyen verkkokauppiaan näkökulmaan. Tutkimuksen tulokset osoittavat, että suoratoimitusmalli tarjoaa merkittäviä kustannussäästöjä, sillä se eliminoi tarpeen varastoinnille. Tämä vähentää verkkokaupan kiinteitä kuluja, sitoutunutta pääomaa ja liiketoimintariskiä. Lisäksi suoratoimitus mahdollistaa laajan tuotekirjon ilman suurta alkupääomaa. Toisaalta tutkimuksessa havaittiin, että suoratoimitusmalliin liittyy keskeisiä haasteita, kuten toimitusketjun hallinnan menettäminen ja pienet katteet, jotka heikentävät verkkokaupan kannattavuutta. Haasteena on myös tilausten pirstoutuminen, jossa tilatut tuotteet toimitetaan asiakkaalle eri jakelijoilta eri ajankohtina, mikä kasvattaa toimituskustannuksia ja pidentää toimitusaikoja, heikentäen entisestään verkkokaupan katteita ja asiakastyytyväisyyttä. Johtopäätöksenä todetaan, että suoratoimitus on houkutteleva vaihtoehto pienyrityksille ja alan uusille toimijoille, jotka haluavat aloittaa verkkokauppaliiketoiminnan mahdollisimman pienellä riskillä ja alkupääomalla. Menestys verkkokauppamarkkinoilla on kuitenkin haastavaa, sillä suoratoimitusmalli edellyttää huolellista jakelijasuhteiden hallintaa sekä tehokasta markkinointia sosiaalisen median alustoilla, jotta suoratoimittaja erottuisi kilpailijoistaan.
Techniques for automatic workability measurement of concrete
(2022-04-25) Suominen, Mikke; Ojala, Teemu; Insinööritieteiden korkeakoulu; Punkki, Jouni
Concrete is one of the most utilized building materials in the construction industry. Concrete structure requirements can be divided into short-term and long-term requirements. The short-term requirements include the plastic state requirements of the fresh concrete, which are usually referred to as a workability. On the other hand, the long-term requirements include, such as strength and durability of the hardened concrete. The short-term requirements affect the long-term requirements and thus it is important to understand the short-term requirement workability. Workability, or more precisely workability characteristics, are often measured by single-point tests that are manual and labour intensive. The aim of this thesis was to research automated techniques to predict concrete workability. In the experimental work, the workability was investigated by monitoring power demand of the laboratory mixer and comparing the results to traditional single-point tests, namely, slump, and flow table tests. Furthermore, the thesis investigated the effects of the most common parameters affecting the workability, which were air content, water content, and superplasticizer amount The study showed the feasibility of the mixer power demand data as a tool to obtain curves and to predict changes in the fresh concrete mixed. However, the results were nonconclusive, as the mixer power demand data did not demonstrate high accuracy when predicting manual single-point workability classes. Therefore, the power data alone was unsatisfactory, but could be investigated together with other known automated methods, such as machine or deep learning. Furthermore, the study showed how different parameters of the fresh concrete affect the mixing power and clarified questions for future automatic measurement methods.
Use of electrical impedance spectroscopy for online monitoring of concrete compaction
(2020-06-15) Ahmed, Hassan; Ojala, Teemu; Insinööritieteiden korkeakoulu; Punkki, Jouni
Compaction of concrete is a crucial on-site step that enables concrete to reach design strength and density. This process is generally carried out using vibrators that pack the aggregates together and expel the entrapped air from the concrete element. Proper compaction ensures that all the entrapped air escapes the concrete without causing segregation. Based on the duration of vibration concrete can be under-vibrated, well-vibrated, or over-vibrated. Under-vibrated concrete causes many durability problems, such as: honey-combing, cold joints, and subsidence cracking. On the other hand, over-vibration of concrete leads to segregation and probable failure of the concrete element. Typically, compaction is subjectively monitored by personnel on site, which is insufficient to obtain a well-vibrated concrete. This thesis investigates the use of Electrical Impedance Spectroscopy (EIS) to monitor concrete compaction during vibration. Concrete can be divided into a resistive part and a conductive part, where the first is the cement paste and water-filled voids, while the latter is the air voids as well as the aggregates. An electrode panel was designed to investigate top, middle, and bottom layers of tested concretes. This panel was fitted inside a plexiglass mould where seven samples of the same concrete mix were tested. Three vibration dura-tions were chosen to obtain under-, over-, and well-vibrated concretes. Alternating current was sent at different frequencies using an impedance analyzer, and the resistance of each layer was obtained through analyzing the measured reactance and resistance of concrete. Followingly, three cores were drilled form each hardened concrete sample and the densities of these cores were statically analyzed to check for segregation. Additionally, vertical sections were cut to visually inspect the distribution of aggregates and air voids inside the concrete. Analysis of the data showed that segregation could be detected by studying the variance of the resistance values for different layers during compaction. The top and middle layer showed a significant resistance decrease, whereas an increase was noted in the bottom layer. This change was linked to the observed segregation in the cut vertical segments, where the bottom layer had a higher amount of accumulated aggregates compared with the other two layers. Additionally, statistical analysis was carried out on the drilled cores densities, which showed a large variance in values denoting segregation. Further analysis was carried out comparing the difference between the resistance of top and bottom layers over the vibration duration. It was found that all segregated samples passed a limit of dif-ference in those EIS obtained resistances compared with the unsegregated sample.

Browsing by Author "Ojala, Teemu"

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