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Monitoring concrete mixing process

Introduction

Being one of the most versatile building materials, concrete is used in many forms of construction. Concrete is often used in residential driveways, house foundations, walls, as well as many other uses. It is made by mixing cement, water, coarse and fine aggregates. Mixing is the most fundamental step in the manufacture of concrete. Mixing concrete may or may not be a precision operation depending on the application. For applications such as building a containment bunker for accumulating waste, precision is not very important. For critical applications like building a skyscraper, quality control requirements are very high.

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Application

There are two main categories of mixer: batch mixers and continuous mixers. Batch mixers produce concrete one batch at a time, while continuous mixers produce concrete at a constant rate. Irrespective of the mixer, rheological properties of the prepared concrete, mainly viscosity, is critical for concrete industry since it affects placement and workability. It influences the productivity and quality of concrete, including mechanical properties and durability. Monitoring of viscosity during the mixing process is needed to detect if the desired mix consistency has been achieved. It can help control the quality of fresh concrete and ensure sustainability of concrete structures.

Why is viscosity management critical in concrete mixing?

The broad and significant factors which make viscosity management important in concrete mixing:

  1. Quality: Final viscosity of the concrete mix is critical, since it affects placement, durability and sustainability of the concrete structure. Under mixing will give rise to non-homogeneity, so correct viscosity measurements can detect in real time, the state of the mixture.
  2. Waste: Over-mixing can not only change the state of end product but is a waste of time and energy. Viscosity management in the concrete mixing process can enable identifying the endpoint reliably and accurately, thus leading to significant reduction in rejects and wastes.
  3. Efficiency: Hassle free, real time monitoring of concrete mix viscosity can save a lot of time and effort which is involved in offline analysis of the sample and making process decisions based on that analysis.
  4. Environment: Lowering the amount of wastes is good for the environment.

To ensure the change in concrete viscosity through-out the process stream is monitored in real time, making measurements from a baseline rather than simply measuring absolute values, and making viscosity adjustments by adjusting solvents and temperature to keep it within specified limits.

Challenges

Concrete mixing operators recognize the need to monitor viscosity but making that measurement has challenged process engineers and quality departments over the years.

Challenges with Off-line viscosity measurements

Existing laboratory viscometers are of little value in process environments because viscosity is directly affected by temperature, shear rate and other variables that are very different off-line from what they are in-line. Collecting samples to be tested in the laboratory and making process decisions based on the findings in the laboratory can be highly cumbersome, time-consuming and extremely inefficient. It is pretty inaccurate, inconsistent and non-repeatable even with an experienced operator.

Challenges with Rotational viscometers

Rotational viscometer measures concrete viscosity by monitoring the torque required to rotate a spindle at a constant speed within the fluid. The viscosity measurement principle is as follows – the torque, generally measured by determining the reaction torque on the motor, is proportional to the viscous drag on the spindle, and thus to the viscosity of the fluid. This technique however poses more problems than it solves:

  • Torque monitoring is carried out by measuring the supply current during the mixing process. Fluctuations in supplied power to the motor renders the measurements completely unreliable, making is difficult to keep costs at a controllable level and generates higher quantities of waste concrete. Controlling power fluctuations by switching to a more reliable power supply in form of a generator can be a very expensive option.
  • Because the spindle is rotating, the wires attached to the torque sensor on the shaft would wind up and snap. Slip rings can be alternatives, but not ideal because of set-up times, costs and inevitable wear and tear.

Rheonics' Solutions

Automated and continuous in-line viscosity measurement is crucial to concrete mix. Rheonics offers the following solutions for the concrete mixing process:

  1. In-line Viscosity measurements: Rheonics’ SRV is a is a wide range, in-line viscosity measurement device with inbuilt fluid temperature measurement and is capable of detecting viscosity changes within any process stream in real time.
  2. In-line Viscosity and Density measurements: Rheonics’ SRD is an in-line simultaneous density and viscosity measurement instrument with inbuilt fluid temperature measurement. If density measurement is important for your operations, SRD is the best sensor to cater to your needs, with operational capabilities similar to the SRV along with accurate density measurements.

Automated in-line viscosity measurement through SRV or an SRD eliminates the variations in sample taking and lab techniques which are used for viscosity measurement by the traditional methods. Rheonics’ sensors are driven by patented torsional resonators. Rheonics balanced torsional resonators together with proprietary 3rd generation electronics and algorithms make these sensors accurate, reliable and repeatable under the harshest operating conditions. The sensor is located in-line so that it continuously measures the concrete mix viscosity. The consistency of the concrete mix can be ensured by automation of the dosing system through a controller using continuous real-time viscosity measurements. Both the sensors have a compact form factor for simple OEM and retrofit installation. They require no maintenance or re-configurations. Using no consumables, SRV and SRD are extremely easy to operate.

Rheonics' Advantage

Compact form factor, no moving parts and require no maintenance

Rheonics’ SRV and SRD have a very small form factor for simple OEM and retrofit installation. They enable easy integration in any process stream. They are easy to clean and require no maintenance or re-configurations.

Insensitive to mounting conditions: Any configuration possible

Rheonics SRV and SRD use unique patented co-axial resonator, in which two ends of the sensors twist in opposite directions, cancelling out reaction torques on their mounting and hence making them completely insensitive to mounting conditions. Hook up the sensor in different parts of the mixing tank and check the consistency of the mix throughout the process. These sensors can easily cope up with regular relocation.

Complete system overview and predictive control – monitor the mixing process with extreme ease

Rheonics’ software is powerful, intuitive and convenient to use. Real-time ink viscosity can be monitored on a computer. Multiple sensors are managed from a single dashboard spread across the factory floor.

Wide operational capabilities

Rheonics’ instruments are built to make measurements in the most challenging conditions. SRV has the widest operational range in the market for inline process viscometer:

  • Pressure range up to 5000 psi
  • Temperature range from -40 up to 200°C
  • Viscosity range: 0.5 cP up to 50,000 cP

Achieve the right mix properties, cut down costs and enhance productivity

Rheonics’ closed loop process systems cater to the needs of today’s environmental and safety concerns. Integrate an SRV/SRD in the mixing tank and monitor the viscosity of the mixture all the way till it achieves the desired viscosity SRV (and SRD) constantly monitors and controls viscosity (and density in case of SRD) and prevents overuse of resources. Optimise the mixing process with an SRV and experience lesser reject rates, lesser wastes, fewer customer complaints, fewer press shut downs and material cost savings– produce exacting results safely and profitably. Avoid future liabilities and litigation costs, achieve a better bottom line.

Superior sensor design and technology

Sophisticated, patented 3rd generation electronics drive these sensors and evaluate their response. Ultra-fast and robust electronics, combined with comprehensive computational models, make Rheonics devices one of the fastest and most accurate in the industry. SRV and SRD give real time, accurate viscosity (and density for SRD) measurements every second and are not affected by flow rate variations!

SRV is available with industry standard process connections like ¾” NPT and 1” Tri-clamp allowing operators to replace an existing temperature sensor in their process line with SRV giving highly valuable and actionable process fluid information like viscosity besides an accurate measurement of temperature using an in-build Pt1000 (DIN EN 60751 Class AA, A, B available).

Electronics built to fit your needs

Available in both an explosion-proof transmitter housing and a small-form factor DIN rail mount, the sensor electronics enables easy integration into process pipelines and inside equipment cabinets of machines.

 

Easy to integrate

Multiple Analog and digital communication methods implemented in the sensor electronics makes connecting to industrial PLC and control systems straightforward and simple.

 

Implementation

Directly install the sensor to your process stream to do real time viscosity and density measurements. No bypass line is required: the sensor can be immersed in-line, flow rate and vibrations do not affect the measurement stability and accuracy. Optimize mixing performance by providing repeated, consecutive, and consistent tests on the fluid.

Rheonics Instrument Selection

Rheonics designs, manufactures and markets innovative fluid sensing and monitoring systems. Precision built in Switzerland, Rheonics’ in-line viscometers has the sensitivity demanded by the application and the reliability needed to survive in a harsh operating environment. Stable results – even under adverse flow conditions. No effect of pressure drop or flow rate. It is equally well suited to quality control measurements in the laboratory.

Suggested product(s) for the Application

  • Wide viscosity range – monitor the complete process
  • Repeatable measurements in both Newtonian and non-Newtonian fluids, single phase and multi-phase fluids
  • Hermetically sealed, all stainless steel 316L wetted parts
  • Built in fluid temperature measurement
  • Compact form-factor for simple installation in existing process lines
  • Easy to clean, no maintenance or re-configurations needed
  • Single instrument for process density, viscosity and  temperature measurement
  • Repeatable measurements in both newtonian and non-newtonian fluids, single phase and multi-phase fluids
  • All metal (316L Stainless Steel) construction
  • Built in fluid temperature measurement
  • Compact form-factor for simple installation in existing pipes
  • Easy to clean, no maintenance or re-configurations needed
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