Page 4 - November-2022

TECHNICAL PAPER

LATE AGE MECHANICAL

STRENGTHS AND HYDRATION

OF ULTRA HIGH PERFORMANCE

CONCRETE BLENDED WITH

METAKAOLIN AND HIGH VOLUME ZONGYUN MO

LIMESTONE YOUMIN HAN
JIAWEI WANG
LI JIANG*

Abstract on improving mechanical and durability properties of UHPC
ascribed to its active reaction and filling effect. Silica fume can
In this study, late age re-hydration for metakaolin (MK) added generally assume the office of reactive powder when preparing
ultra high performance concrete (UHPC) with water curing UHPC on account of its ultra high specific area and pozzolanic
from 90 to 365 days were investigated. And limestone (LS) was activity [1-4] . However the preparation of UHPC incorporated silica
also incorporated into UHPC replacing 30 % cement by binder fume is expensive due to the high cost of silica fume. Therefore,
mass for reducing the cement usage. In addition, cement many researchers in the world started to search for other kinds
and LS cement specimens without MK were prepared as the of supplementary reactive powders such as rice husk ash [5-7] ,
references. Mortar specimens were employed for testing the metakaolin (MK) [8-13] , fly ash, slag powder as well as glass
[14]
compressive and flexural strength at 90, 150, 210, 270, and powder [15] , et al., which can be obtained at lower cost or lesser
365 days. And paste specimens were used to measure the hazard on the environment. For example, MK is an excellent
chemically bound water, differential thermal analysis (DTA) pozzolanic material used in concrete. It can be derived from
curves, X-ray diffraction (XRD) patterns, pore structures, and kaolin clay rich in earth’s crust by dehydration under 500-800°C,
micro-morphology at designated ages. Results indicate that which consumes less energy and emits hardly any carbon dioxide
the re-hydration causes an increasing tendency for strength of compared to the preparation of cement [16-17] . Moreover, the
mortars from 90 to 270 days while a decreasing tendency after compressive strengths and durability of UHPC incorporated with
270 days. The re-hydration degree for MK contained mixtures MK are satisfactory compared with that of UHPC blended with
are obviously lower than that of the references. MK can stabilize silica fume [8-9] .
the late age mechanical property and micro-structure of water Also alternative products that are low-carbon dioxide emitting
cured UHPC. Moreover, the combination of LS and MK do not and environmentally-friendly supplementary materials of
obviously degrade the strength and micro-structure of long term cement such as limestone, glass powder, fly ash, etc. have been
water cured UHPC compared with that of binary MK contained widely used in UHPC for alleviating energy consumption and
mixture. environment pollution related to the high usage of cement [18-20] .
It is demonstrated that its cement hydration degree in UHPC
Keywords: Limestone; Metakaolin; Microstructure; was only 30-35 % [21] . Therefore, the UHPC with high volume
Re-hydration; Strength; UHPC.
LS replacing cement (a maximal level of 50 %) still can attain
comparative compressive strength with normal UHPC without
1. INTRODUCTION LS [22] . In addition, replacement of cement with LS can accelerate
cement hydration due to increasing water to cement ratio (w/c)
Recently, ultra high performance concrete (UHPC) with an by the dilution effect of limestone (LS) in UHPC [18, 22] .
exceptional homogeneous and compacted microstructure has
been studied extensively around the world due to its particular In normal environment, the hydration rate of UHPC paste is
superiority such as ultra high strength and durability. Among negligible at late ages owing to few residual free water [18] .
selected raw materials of UHPC, the reactive powder with ultra However if the concrete matrix is under long term water curing
high specific area and pozzolanic activity plays a crucial effect condition, its late age hydration rate of paste may be impressive.

18 THE INDIAN CONCRETE JOURNAL | NOVEMBER 2022
*Corresponding author : Li Jiang, Email: jl@ahpu.edu.cn