Papers by Djwantoro Hardjito
Berbagai penelitian mengenai pemanfaatan material lumpur Sidoarjo, khususnya sebagai material pen... more Berbagai penelitian mengenai pemanfaatan material lumpur Sidoarjo, khususnya sebagai material pengganti semen (pozzolan) telah dilakukan. Penelitian ini berfokus pada penggunaan lumpur Sidoarjo dengan kadar yang tinggi, yaitu >50%, serta membandingkan hasil tersebut dengan fly ash. Analisa terhadap material dilakukan menggunakan XRF (X-Ray Flouresence) untuk mengetahui karakteristik dari material tersebut. Analisa juga dilakukan terhadap pengaruh ukuran butiran menggunakan PSA (Particle Size Analysis). Lumpur dilakukan treatment dari pengeringan, pembakaran hingga digiling menggunakan bar-mill dengan lama penggilingan bervariasi untuk mendapatkan ukuran butiran berbeda. Presentase kadar yang digunakan adalah 50%, 55% dan 60% dari total cementitious material. Mortar dan beton digunakan ukuran 5x5x5 cm 3 dan 15x15x15 cm 3 lalu dilakukan pengujian berupa kuat tekan, workability dan setting time. Hasil menunjukkan semakin halus ukuran butiran, semakin tinggi kuat tekan dan workability-nya. Di antara kadar 50%-60% penggantian semen dengan lumpur Sidoarjo, kadar 50% merupakan yang paling efektif. Pada beton dengan lumpur Sidoarjo menghasilkan slump test sebesar 8,5 cm dengan kuat tekan 34,07 MPa pada umur 37 hari.
Materials Science Forum, 2014
Previous studies on Sidoarjo volcanic mud have been largely focusing on its use as low-volume cem... more Previous studies on Sidoarjo volcanic mud have been largely focusing on its use as low-volume cement replacement pozzolanic material and not as a high-volume cement replacement material. This study is intended to study the behaviour of fresh mortar incorporating Sidoarjo volcanic mud as cement replacement in high-volume i.e. 50%, 55% and 60%; and compares the results with the ones of high-volume fly ash mortar. Calcination and grinding were applied as pre-treatment for the mud to make it more reactive. Grinding time was varied into three different grinding time periods from two to eight hours, to vary the particle sizes of the calcined mud. The results show that the finer the particle size of the Sidoarjo volcanic mud, the bigger the flow of the fresh mortar. The flow of fresh mortar containing the Sidoarjo mud is lower compared to those of the ones with fly ash.
International Journal of Construction Education and Research, Aug 8, 2019
A common method used to increase the strength of concrete is to add more cement to reduce the wat... more A common method used to increase the strength of concrete is to add more cement to reduce the water-to-cement ratio. However, this is not always acceptable as adding more cement increases autogenous shrinkage, thermal and shrinkage cracking, and the cost of concrete production. By appropriately using superplasticizers, highperformance low cement concrete (LCC) can be produced. This study explores the potential of LCC by limiting cement content, adding alternative cementitious materials, and superplasticizers. Data was collected from the outcome of an annual National Student Concrete Competition conducted in Indonesia over three consecutive years. The new concept of LCC mix design was explained to all participants, i.e., civil engineering students, before they made their concrete specimens. Following the competition, all mixture compositions and their resulting concrete properties were analyzed. It was found that the participants' knowledge on the use of superplasticizer and cementitious materials was the most notable challenge. Nevertheless, they discovered that making LCC is a possibility. Concrete with a compressive strength of 50 MPa (7252 psi) can be made using cement content as low as 200 kg/m 3 (337 lb/yd 3 ) with sufficient workability. Furthermore, the effect of several factors on the performance LCC is described in this study.
Iranian Journal of Science and Technology, Transaction of Civil Engineering, 2024
The utilization of fly ash as a waste product of coal combustion is currently limited to being a ... more The utilization of fly ash as a waste product of coal combustion is currently limited to being a supplementary cementitious material (SCM). Fly ash integrates well with cement, demonstrating favorable qualities in concrete such as good workability, high ultimate strength, and durability. However, the use of fly ash in very high proportions has not been extensively explored due to its weakness in early strength development in concrete. Methods have been investigated to enhance the early compressive strength and compressive strength of very-high-volume fly ash mortar. This research explores the incorporation of fly ash at a very high percentage (80%), also known as very-high-volume fly ash (VHVFA), into mortar using low-molarity alkali solution and thermal activation. The activation of fly ash is examined through alkali activation, specifically utilizing sodium hydroxide (NaOH) solution, and thermal activation involving temperature and activation time. Pre-activating Class F fly ash for 2 hours using a 0.3 M NaOH solution at a temperature of 60°C increased the early compressive strength (at 7 days) by 35% and the compressive strength at 28 days by 12%. Pre-activation for 30 minutes at room temperature with a 1 M NaOH activator was able to increase the early compressive strength of VHVFA mortar (at 7 days) by 79% for Class C fly ash and by 43% at 28 days. In this study, it is shown that through the use of low-molarity alkali solution and thermal activation, the compressive strength of VHVFAmortar can be increased whether using Class F fly ash or Class C fly ash.
Jurnal Teknologi
Fly ash, a waste material derived from the coal burning in power plants, could be utilized in con... more Fly ash, a waste material derived from the coal burning in power plants, could be utilized in concrete mixtures as a filler or as a cement replacement material, either partially or fully. Some papers also report that high-calcium fly ash can be utilized as a cementitious material through the hydration process. However, there are just a few papers that studied the behavior of concrete that utilizes high-calcium fly ash as the sole binder material without any chemical activators. Furthermore, there are no reports about whether the effect of the different water-to-cementitious ratios of this concrete is the same as the ordinary Portland cement concrete. This paper presents an initial development on the use of fly ash as a sole binder material, i.e., 100% fly ash concrete without any chemical solution as an activator. This research utilizes the high calcium content in the fly ash to produce concrete with a commonly used method (just add the water without any alkali activator) and invest...
SP-222: Seventh CANMET/ACI International Conference on Recent Advances in Concrete Technology, 2004
Abstract: This paper presents the effect of mixture composition on the compressive strength of fl... more Abstract: This paper presents the effect of mixture composition on the compressive strength of fly ash-based geopolymer concrete. Test results show that water-to-sodium oxide (H2O-to-Na2O) molar ratio and the water-to-geopolymer solids ratio by mass influence the compressive strength of fly ash-based geopolymer concrete. The compressive strength decreases when these ratios increase. However, the sodium oxide-to-silicon oxide (Na2O-to-SiO2) molar ratio of the geopolymer mixture does not have any significant effect on the ...
Clinical and Experimental Dermatology, 2020
Circulating fluidized bed combustion (CFBC) is a newer type of burner that employ a circulating p... more Circulating fluidized bed combustion (CFBC) is a newer type of burner that employ a circulating process to burn fuel effectively. CFBC burning process is gaining more popularity due to its compact size, high efficiency and lower burning temperature compared to the pulverized coal combustion (PCC) burner. The CFBC burner produces fly ash with different physical properties compared to the PCC burner, i.e. the fly ash is not rounded, and required higher water content for comparable workability. The CFBC fly ash also has a high sulfur content that is detrimental for hardened concrete. Due to its drawbacks, the CFBC hardly used as cementitious material and geopolymer precursor. This study focuses on comparing variations in the concentration of NaOH solution and variations in the ratio of alkaline activators to the setting time and compressive strength of geopolymer mortars on a new class of CFBC fly ash, which have low sulfur content. The concentrations of NaOH solution were 6M, 8M, 10M,...
Fly ash merupakan limbah industri yang sering digunakan untuk menggantikan Portland Cement dalam ... more Fly ash merupakan limbah industri yang sering digunakan untuk menggantikan Portland Cement dalam pembuatan beton. Fly ash tersedia dalam jumlah banyak dan penggunaannya masih terbatas. Namun penggunaan fly ash tipe C dengan kandungan kalsium yang tinggi bisa menyebabkan terjadinya flash set dimana beton geopolimer mengeras dengan sangat cepat. Penelitian sebelumnya membuat prosedur pembuatan mortar geopolimer berbahan dasar fly ash tipe C dengan urutan yang berbeda dan menghasilkan beton yang sedikit lebih baik jika dibandingkan dengan prosedur pada umumnya. Penelitian ini bertujuan untuk menganalisa pengaruh prosedur mix design terhadap karakteristik mortar geopolimer. Berdasarkan hasil penelitian didapatkan dengan mencampurkan fly ash terlebih dahulu dengan larutan NaOH selama 5 menit dan kemudian ditambahkan dengan larutan sodium silikat akan menghasilkan mortar dengan kuat tekan yang tinggi setelah dilakukan curing oven pada suhu 60 oC selama 24 jam. Begitu pula dengan prosedur ...
Perkembangan fly ash sebagai bahan pengganti semen saat ini sudah banyak digunakan khususnya pada... more Perkembangan fly ash sebagai bahan pengganti semen saat ini sudah banyak digunakan khususnya pada beton geopolimer. Fly ash tipe C dengan kandungan CaO yang tinggi bila digunakan sebagai material dasar geopolimer dapat menyebabkan terjadinya flash setting atau pengerasan beton yang sangat cepat namun juga dapat meningkatkan kekuatan tekan pada beton geopolimer. Hal ini dapat menimbulkan masalah apabila digunakan sebagai bahan dasar beton geopolimer dalam skala yang besar yang memerlukan setting time yang cukup lama. Kandungan CaO dapat diindikasikan dengan nilai pH fly ash sehingga penelitian ini menggunakan larutan asam untuk menurunkan nilai pH awal dari fly ash. Berdasarkan hasil penelitian, didapatkan bahwa penambahan larutan asam pada fly ash dapat menyebabkan pH awal fly ash berkurang namun initial setting time yang didapatkan justru bertambah cepat ± 40-60%. Initial setting time yang paling cepat dialami fly ash yang ditambahkan dengan larutan asam klorida (HCl). Selain itu, ...
Geopolimer dibuat dengan mencampurkan dua bahan dasar yakni fly ash dan alkali activator. Penelit... more Geopolimer dibuat dengan mencampurkan dua bahan dasar yakni fly ash dan alkali activator. Penelitian-penelitian terdahulu menggunakan fly ash tipe C sebagai bahan dasarnya dan pada penelitian kali ini menggunakan fly ash dari PLTU Ngoro yang memiliki tipe F. PLTU ini memiliki sitem pembakaran Circulating Fluidized Bed (CFB), di mana karakteristik fly ash yang dihasilkan berbeda dengan fly ash PLTU pada umumnya, yang memakai sistem Pulverized Coal Combustion (PCC). Perbedaan karakteristik diakibatkan perbedaan kualitas batu bara dan suhu pembakaran. Penelitian ini bertujuan untuk menganalisa potensi fly ash Ngoro dan pengaruh sodium silikat terhadap kuat tekan, workability, dan setting time geopolimer. Kadar molaritas NaOH yang digunakan adalah 8M sampai 14M. Campuran dibagi menjadi tiga tahap yaitu tahap pertama dengan perbandingan massa sodium silikat:NaOH(solid) 2,5; Tahap kedua dan ketiga ditentukan berdasarkan hasil tahap pertama. Tahap pertama menunjukkan kuat tekan sebesar 37,...
Beton geopolimer merupakan beton yang berbahan dasar material yang kaya akan unsure alumina (Al) ... more Beton geopolimer merupakan beton yang berbahan dasar material yang kaya akan unsure alumina (Al) dan silica (Si). Salah satu material yang bisa digunakan adalah fly ash. Namun, penggunaan fly ash dengan tipe C bisa berakibat pada situasi flash set di mana beton mengeras dengan cepat. Mengatasi masalah ini, digunakan boraks sebagai bahan tambahan dalam larutan alkali agar memperlambat setting time dan juga menggunakan kalsium oksida (CaO) agar membantu peningkatan kuat tekan beton geopolimer. Dari hasil penelitian, menunjukkan bahwa penambahan boraks pada larutan alkali memberi pengaruh terhadap setting time. Penambahan boraks bisa memperlambat setting time sesuai dengan jumlah kadar boraks yang ditambahkan. Penambahan boraks cenderung menurunkan kuat tekan beton namun, bergantung pada karakteristik fly ash yang digunakan. Penggantian sebagian fly ash dengan kalsium oksida (CaO) memberi pengaruh peningkatan kuat tekan pada beton geopolimer.
Pembangunan dalam bidang konstruksi di Indonesia sedang berkembang, agar tidak merusak keseimbang... more Pembangunan dalam bidang konstruksi di Indonesia sedang berkembang, agar tidak merusak keseimbangan ekosistem akibat proses konstruksi maka pembangunan berkelanjutan sangat diperlukan. Penggunaan material-material yang bersifat tidak merusak alam dan pemanfaatan limbah sebagai material konstruksi harus dilakukan. Bottom ash dan fly ash merupakan limbah hasil pembakaran PLTU yang masih dapat digunakan sebagai material pembuatan beton. Dalam dunia konstruksi pemanfaatan fly ash sudah dilakukan, sedangkan untuk bottom ash masih sangat jarang padahal bottom ash mempunyai potensi untuk menggantikan pasir sebagai agregat halus dalam beton. Dalam penelitian ini, bottom ash akan diberi treatment berupa pencucian dan pencampuran antara bottom ash kasar dan halus hingga mencapai kepadatan maksimum sebelum akhirnya digunakan untuk membuat beton High Volume Fly Ash (HVFA). Pengujian slump dan kuat tekan akan dilakukan pada beton HVFA. Dari penelitian ini, dihasilkan bahwa treatment pencucian bo...
In geopolymer concrete, a by-product material rich in silicon and aluminum (low calcium fly ash) ... more In geopolymer concrete, a by-product material rich in silicon and aluminum (low calcium fly ash) is chemically activated by a high alkaline solution to form a paste that binds the loose coarse and fine aggregates, as well as other un-reacted materials in the mixture. This paper presents the results of an experimental study on the behavior and the strength of twelve geopolymer concrete slender columns under equal load eccentricities. The primary variables of the test series were concrete compressive strength, longitudinal reinforcement ratio, and load eccentricity. The test results gathered included the deflection and the load capacity of the columns. The test failure loads were compared with the values calculated by the methods currently available for Ordinary Portland Cement (OPC) concrete. Excellent correlation between experimental and analytical results is found.
Iranian Journal of Science and Technology, Transactions of Civil Engineering, 2019
IOP Conference Series: Materials Science and Engineering, 2019
The problem of rapid or short setting time has been reported by many researchers when utilizing h... more The problem of rapid or short setting time has been reported by many researchers when utilizing high calcium fly ash as an aluminosilicate source material in the synthesis of geopolymers. Meanwhile, there are very few studies carried out to overcome this obstacle. This study was conducted to evaluate the cooling treatment of the alkaline solution to prolong the setting time of the geopolymer. Alkaline solutions with five different temperatures were used to synthesize the geopolymer paste. Each set of fresh geopolymer paste was tested using the Vicat apparatus according to ASTM C191 to measure its setting time. The results showed that a decrease in the temperature of the alkaline solutions prolonged both the initial and the final setting time of the geopolymer paste. An alkaline solution with a temperature of 9°C could double the initial setting time compared to the control mixture (31°C). In the mortar phase, the cooling treatment also increased the compressive strength of the geopolymer mortar besides longer setting time.
AIP Conference Proceedings, 2017
There are more than four decades since the last 1970s where geopolymers concrete was first introd... more There are more than four decades since the last 1970s where geopolymers concrete was first introduced and developed to use as a replacement to conventional concrete material which uses cement as a binder. And since the last two decades, geopolymers which utilized fly ash as aluminosilicate source material, i.e. fly ash based geopolymers, have been investigated. Many researchers present how to produce the best fly ash based geopolymer with a various source of constituent material as well as mixing formula to achieve exceptional concrete performance. Although there is a similar trend towards factors affecting the result of fly ash based geopolymer synthesis, there is still remain a wide range in mixture proportion. The considerable variation in fly ash characteristics as source material in the synthesis can very likely be one of the causes of this problem. This paper attempts to identify the effect of source material variation of geopolymer concrete, particularly which use fly ash as source material and focuses on the variation of its characteristics and the effects to properties of concrete. From the reviews it concluded that different sources (and even the same source, but different batch) of fly ash materials will give some different characteristics of the fly ash, where it would affect the synthesis process of the fly ash based geopolymer concretes.
Materials Science Forum, 2016
Geopolymer that was made with high CaO content fly ash was found to have higher compressive stren... more Geopolymer that was made with high CaO content fly ash was found to have higher compressive strength than the low CaO fly ash, using the same mixture composition. This effect could be due to the physico-chemical properties of the fly ash, in respect to its particle size or the chemical composition. Although it was not widely published, the occurrence of flash setting of geopolymer was known to occur when using high CaO content fly ash as the precursor. Geopolymer paste may solidify within minutes after the addition of alkali activators, making it very difficult to cast in big volume. This paper investigate the effect of borax addition to the high calcium fly ash-based geopolymer mixture to reduce the occurrence of flash setting. It was found that the setting time can be extended significantly, with the addition of 5% borax, by mass, of fly ash. The addition of borax also have positive effect on increasing the compressive strength of geopolymer.
Materials Science Forum, 2016
This study was conducted to determine the factors that may affect the compressive strength of fly... more This study was conducted to determine the factors that may affect the compressive strength of fly ash-based geopolymer. With so many kinds of fly ash available and has its different characteristics, it would be very influential on geopolymer produced. These effects is classified into internal and external of the fly ash material. Internal influences include the physical and chemical properties of the fly ash, while external influences associated with mixture of geopolymer and the manufacturing process. From the experiment results, it was found that the size of the granules, the content of CaO and MgO, and carbon content in fly ash that are internal factors that may affect the compressive strength. While the ratio of sodium silicate and sodium hydroxide in the alkaline solution and NaOH molarity used can also give a direct influence on the compressive strength of geopolymer.
Materials Science Forum, 2016
Fly ash is a waste from coal burning, that are generated with fluctuation both in its physical an... more Fly ash is a waste from coal burning, that are generated with fluctuation both in its physical and chemical characteristics. This characteristics of fly ash when used in the making of geopolymer concrete will greatly affect the final products obtained. The pH value measured in fly ash, according previous research, can influence the setting time of geopolymer and fly ash with high pH values can cause flash-setting in the concrete. Understanding more clearly about the factors that affect the setting time of fly ash based geopolymer is important for further progress and development of the material. It was found that factors that influence the setting time of geopolymer was not only from the physical and chemical properties of the fly ash itself. Other factors such as composition and mix design, manufacturing process and environmental conditions can also affect its setting time. The experimental results showed that fly ash particle size, CaO and MgO content, in addition to ratio of sodi...
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Papers by Djwantoro Hardjito